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Full text of "ASCE 7: Minimum Design Loads for Buildings and Other Structures"

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By Authority Of 

THE UNITED STATES OF AMERICA 

Legally Binding Document 



By the Authority Vested By Part 5 of the United States Code § 552(a) and 
Part 1 of the Code of Regulations § 51 the attached document has been duly 
INCORPORATED BY REFERENCE and shall be considered legally 
binding upon all citizens and residents of the United States of America. 
HEED THIS NOTICE : Criminal penalties may apply for noncompliance. 




Document Name 



CFRSection(s): 



Standards Body: American Society of Civil Engineers 



SEI/ASCE 7-02 
Second Edition 



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mWMMM 



American Society of Civil Engineers 

Minimum Design Loads for 
Buildings and Other Structures 

Revision of ASCE 7-98 

This document uses both Systeme International (SI) units and customary units. 



Structural Engineering Institute 



SEI/ASCE 7-02 
Second Edition 



American Society of Civil Engineers 

Minimum Design Loads 
for Buildings and 
Other Structures 



This second edition incorporates the 

corrections as shown in the errata 

found on www.seinstitute.org. 



Revision of ASCE 7-98 



This document uses both Systeme international (SI) units and customary units. 





mm\ 



SWlKgMiS 



Structural Engineering Institute 



Published by the American Society of Civil Engineers 

1801 Alexander Beii Drive 

Reston, Virginia 20191-4400 



ABSTRACT 

This revision of the ASCE Standard Minimum Design Loads 
for Buildings and Other Structures is a replacement of ASCE 
7-98. This Standard provides requirements for dead, live, soil, 
flood, wind, snow, rain, ice, and earthquake loads, and their 
combinations that are suitable for inclusion in building codes 
and other documents. 

Substantial changes were made to the wind, snow, 
earthquake, and ice provisions. In addition, substantial new 
material was added regarding the determination of flood 
loads. The structural loading requirements provided by this 
Standard are intended for use by architects, structural 
engineers, and those engaged in preparing and administering 
local building codes. 

Library of Congress Cataloging-in-Publication Data 

Minimum design loads for buildings and other structures / 
American Society of Civil Engineers, 
p. cm. — (ASCE standard.) 
"Revision of ASCE 7-98." 
ISBN 0-7844-0624-3 

1 . Structural engineering — United States. 2. Standards, 
Engineering — United States. I. American Society of Civil 
Engineers. 

TH851 .M56 2002 
624.172 / 021873-dc21 

2002038610 

Any statements expressed in these materials are those of the 
individual authors and do not necessarily represent the views 
of ASCE, which takes no responsibility for any statement 
made herein. No reference made in this publication to any 
specific method, product, process or service constitutes 
or implies an endorsement, recommendation, or warranty 
thereof by ASCE. The materials are for general information 
only. They are not intended as a reference in purchase 
specifications, contracts, regulations, statutes, or any other 
legal document. 

ASCE makes no representation or warranty of any kind, 
whether express or implied, concerning the accuracy, 
completeness, suitability, or utility of any information, 
apparatus, product, or process discussed in this publication, 
and assumes no liability therefore. This information should not 
be used without first securing competent advice with respect 
to its suitability for any general or specific application. Anyone 
utilizing this information assumes all liability arising from such 
use, including but not limited to infringement of any patent or 
patents. 

ASCE and American Society of Civil Engineers — Registered 
in U.S. Patent and Trademark Office. 

Photocopies: Authorization to photocopy material for internal 
or personal use under circumstances not falling within the 
fair use provisions of the Copyright Act is granted by ASCE 
to libraries and other users registered with the Copyright 
Clearance Center (CCC) Transactional Reporting Service, 
provided that the base fee of $1 8.00 per article is paid directly 
to CCC, 222 Rosewood Drive, Danvers, MA 01923. The 
identification for ASCE Books is 0-7844-0624-3/03 $18.00. 
Requests for special permission or bulk copying should be 
addressed to Permissions & Copyright Dept., ASCE. 

Copyright © 2003 by the American Society of Civil Engineers. 

All Rights Reserved. 

Library of Congress Catalog Card No: 2002038610 

ISBN 0-7844-0624-3 

Manufactured in the United States of America. 

Second Printing. 



STANDARDS 



In April 1980, the Board of Direction approved ASCE 
Rules for Standards Committees to govern the writing and 
maintenance of standards developed by the Society. All 
such standards are developed by a consensus standards 
process managed by the Codes and Standards Activities 
Committee (CSAC). The consensus process includes bal- 
loting by the balanced standards committee made up of 
Society members and nonmembers, balloting by the mem- 
bership of ASCE as a whole, and balloting by the public. 
All standards are updated or reaffirmed by the same process 
at intervals not exceeding 5 years. 

The following Standards have been issued: 



ANSl/zw TE 1-82 N-725 Guideline for Design and Analysis 
of Nuclear Safety Related Earth Structures 

ANSI/ASCE 2-91 Measurement of Oxygen Transfer in 
Clean Water 

ANSI/ASCE 3-91 Standard for the Structural Design of 
Composite Slabs and ANSI/ASCE 9-91 Standard Prac- 
tice for the Construction and Inspection of Composite 
Slabs 

ASCE 4-98 Seismic Analysis of Safety-Related Nuclear 
Structures 

Building Code Requirements for Masonry Structures (ACI 
530-02/ASCE 5-02/TMS 402-02) and Specifications for 
Masonry Structures (ACI 530.1-02/ASCE 6-02/TMS 
602-02) 

SEI/ASCE 7-02 Minimum Design Loads for Buildings and 
Other Structures 

ANSI/ASCE 8-90 Standard Specification for the Design of 
Cold-Formed Stainless Steel Structural Members 

ANSI/ASCE 9-91 listed with ASCE 3-91 

ASCE 10-97 Design of Latticed Steel Transmission Struc- 
tures 

SEI/ASCE 11-99 Guideline for Structural Condition 
Assessment of Existing Buildings 

ANSI/ASCE 12-91 Guideline for the Design of Urban 
Subsurface Drainage 

ASCE 13-93 Standard Guidelines for Installation of Urban 
Subsurface Drainage 

ASCE 14-93 Standard Guidelines for Operation and Main- 
tenance of Urban Subsurface Drainage 



ASCE 15-98 Standard Practice for Direct Design of 
Buried Precast Concrete Pipe Using Standard Installa- 
tions (SIDD) 

ASCE 16-95 Standard for Load and Resistance Factor 
Design (LRFD) of Engineered Wood Construction 

ASCE 17-96 Air-Supported Structures 

ASCE 18-96 Standard Guidelines for In-Process Oxygen 
Transfer Testing 

ASCE 19-96 Structural Applications of Steel Cables for 
Buildings 

ASCE 20-96 Standard Guidelines for the Design and 
Installation of Pile Foundations 

ASCE 21-96 Automated People Mover Standards — Part 1 

ASCE 21-98 Automated People Mover Standards — Part 2 

ASCE 21-00 Automated People Mover Standards — Part 3 

SEI/ASCE 23-97 Specification for Structural Steel Beams 
with Web Openings 

SEI/ASCE 24-98 Flood Resistant Design and Construction 

ASCE 25-97 Earthquake- Actuated Automatic Gas Shut-Off 
Devices 

ASCE 26-97 Standard Practice for Design of Buried Precast 
Concrete Box Sections 

ASCE 27-00 Standard Practice for Direct Design of Precast 
Concrete Pipe for Jacking in Trenchless Construction 

ASCE 28-00 Standard Practice for Direct Design of Pre- 
cast Concrete Box Sections for Jacking in Trenchless 
Construction 

SEI/ASCE 30-00 Guideline for Condition Assessment of 
the Building Envelope 

SEI/ASCE 32-01 Design and Construction of Frost- 
Protected Shallow Foundations 

EWRI/ASCE 33-01 Comprehensive Transboundary Inter- 
national Water Quality Management Agreement 

EWRI/ASCE 34-01 Standard Guidelines for Artificial 
Recharge of Ground Water 

EWRI/ASCE 35-01 Guidelines for Quality Assurance of 
Installed Fine-Pore Aeration Equipment 

CI/ASCE 36-01 Standard Construction Guidelines for 
Micro tunneling 

SEI/ASCE 37-02 Design Loads on Structures During Con- 
struction 

CI/ASCE 38-02 Standard Guideline for the Collection and 
Depiction of Existing Subsurface Utility Data 



FOREWORD 



The material presented in this Standard has been pre- 
pared in accordance with recognized engineering principles. 
This Standard should not be used without first securing 
competent advice with respect to its suitability for any 
given application. The publication of the material contained 
herein is not intended as a representation or warranty on 



the part of the American Society of Civil Engineers, or 
of any other person named herein, that this information is 
suitable for any general or particular use or promises free- 
dom from infringement of any patent or patents. Anyone 
making use of this information assumes all liability from 
such use. 



ACKNOWLEDGEMENTS 



The American Society of Civil Engineers (ASCE) 
acknowledges the work of the Minimum Design Loads on 
Buildings and Other Structures Standards Committee of the 
Codes and Standards Activities Division of the Structural 
Engineering Institute. This group comprises individuals 
from many backgrounds including: consulting engineer- 
ing, research, construction industry, education, government, 
design, and private practice. 



This revision of the standard began in 1999 and incor- 
porates information as described in the commentary. 

This Standard was prepared through the consensus 
standards process by balloting in compliance with 
procedures of ASCE's Codes and Standards Activities 
Committee. Those individuals who serve on the Standards 
Committee are: 



Kharaiti L. Abrol 

Robert E. Bachman 

Charles C. Baldwin 

Demirtas C. Bayar 

John E. Breen 

David G. Brinker 

Ray A. Bucklin 

James R. Cagley 

Charles J. Carter 

Jack E. Cermak 

William L. Coulbourne 

Jay H. Crandell 

Stanley W. Crawley 

Majed Dabdoub 

James M. Delahay 

Bernard J. Deneke 

Bradford K. Douglas 

John F. Duntemann 

Donald Dusenberry 

Bruce R. Ellingwood, Vice-Chair 

Edward R. Estes 

Mohammed M. Ettouney 

David A. Fanella 

Lawrence Fischer 

Theodore V. Galambos 

Satyendra K. Ghosh 

Dennis W. Graber 

Lawrence G. Griffis 

David S. Gromala 

Robert D. Hanson 

Gilliam S. Harris 

James R. Harris, Chair 

Joseph P. Hartman 

Scott R. Humphreys 

Nicholas Isyumov 

Christopher P. Jones 

John H. Kapmann, Jr. 

A. Harry Karabinis 

Jon P. Kiland 

Randy Kissell 

Uno Kula 



Edward M. Laatsch 

John V. Loscheider 

Fred Morello 

Ian Mackinlay 

Sanjeev Malushte 

Bonnie Manley 

Harry W. Martin 

Rusk Masih 

George M. Matsumura 

Therese P. McAllister 

Robert R. McCluer 

Richard McConnell 

Kishor C. Mehta 

Joseph J. Messersmith, Jr. 

Joe N. Nunnery 

Michael O'Rourke 

George N. Olive 

Frederick J. Palmer 

Alan B. Peabody 

David B. Peraza 

Clarkson W. Pinkham 

Robert D. Prince 

Robert T. Ratay 

Mayasandra K. Ravindra 

Lawrence D. Reaveley 

Abraham J. Rokach 

James A. Rossberg, Secretary 

Herbert S. Saffir 

Phillip J Samblanet 

Suresh C. Satsangi 

Andrew Scanlon 

Jeffery C. Sciaudone 

William L. Shoemaker 

Emil Simiu 

Thomas D. Skaggs 

Thomas L. Smith 

James G. Soules 

Theodore Stathopoulos 

Donald R. Strand 

Harry B. Thomas 

Wayne N. Tobiasson 



Brian E. Trimble 
David P. Tyree 
Thomas R. Tyson 
Joseph W. Vellozzi 
Francis J. Walter, Jr. 
Yi Kwei Wen 
Peter J.G. Willse 
Lyle L. Wilson 
Joseph A. Wintz, III 

Task Committee on General 
Structural Requirements 
James S. Cohen 
John F. Duntemann 
Donald Dusenberry, Chair 
John L. Gross 
Anatol Longinow 
John V. Loscheider 
Robert T. Ratay 
James G. Soules 
Jason J. Thompson 

Task Committee on Strength 
Bruce R. Ellingwood, Chair 
Theodore V. Galambos 
David S. Gromala 
James R. Harris 
Clarkson Pinkham 
Massandra K. Ravindra 
Andrew Scanlon 
James G. Soules 
Yi Kwei Wen 



Task Committee on Live Loads 
James R. Cagley 
Raymond A. Cook 
Ross B. Corotis 
John V. Loscheider 
William L. Shoemaker 
John G. Tawresey 
Harry B. Thomas 
Thomas R. Tyson 
Yi Kwei Wen, Chair 

Task Committee on Flood Loads 
Christopher P. Jones, Chair 

Task Committee on Wind Loads 

Pete Billing 

Dayrl Boggs 

Jack E. Cermak 

Ronald A. Cook 

Jay H. Crandell 

James M. Delahay 

Bradford K. Douglas 

Charles Everly 

Dennis W. Graber 

Lawrence G. Griffls, Chair 

Gilliam S. Harris 

Peter A. Irwin 

Nicholas Isyumov 

Ahsan Kareem 

Edward M. Laatsch 

Marc Levitan 

John V. Loscheider 

Kishor C. Mehta 

Joseph J. Messersmith, Jr. 

Charles Olivier 

Rick Perry 

Jon A. Peterka 

Timothy A. Reinhold 

Herbert S. Saffir 

Jeffery C. Sciaudone 

Don R. Scott 

William L. Shoemaker 

Emil Simiu 

Douglas Smith 

Thomas L. Smith 

Eric Stafford 

Theodore Stathopoulos 

Peter J. Vickery 

Robert Wills 

Peter J.G. Willse 



Task Committee on Snow and 

Rain Loads 

Charles De Angelis 

Brad Douglas 

Nicholas Isyumov 

J. Randolph Kissell 

Ian Mackinlay 

Joe N. Nunnery 

Michael O'Rourke, Chair 

Edwin R. Schmeckpeper 

Joseph D. Scholze 

W. Lee Shoemaker 

Wayne N. Tobiasson 

Peter J.G. Willse 

Task Committee on Earthquake 

Loads 

Victor Azzi 

Robert E. Bachman, Chair 

David R. Bonneville 

James R. Cagley 

Alan Carr 

Len Cobb 

Michael Constantinou 

Bradford K. Douglas 

Douglas A. Foutch 

Larry D. Franks 

Thomas A. Gangel 

Satyendra K. Ghosh 

John Gillengerten 

Ronald O. Hamburger 

Robert D. Hanson 

James R. Harris 

Ronald W. Haupt 

William T. Holmes 

Douglas G. Honegger 

John Hooper 

Roy J. Hunt 

James K. Iverson 

Martin W. Johnson 

Dominic J. Kelly 

Jon P. Kiland 

Charles A. Kircher 

Vladimir Kochkin 

Edgar V. Leyendecker 

Mike Mahoney 

Sanjeev Malushte 

Bonnie E. Manley 

Harry W. Martin 

Rory M. McGruer, Secretary 

Phillip Myers 



Lawrence D. Reaveley 
James A. Rossberg 
Arthur B. Savery 
Grover L. Sawyer, Jr. 
Timothy D. Sheckler 
Jonathon C. Siu 
James G. Soules 
Harold O. Sprague 
Bill Staehin 
Jason J. Thompson 
John W. Wallace 
Andrew S. Whittaker 
David L. Wismer 

Task Committee on Atmospheric 

Icing 

David G. Brinker 

Peter G. Catchpole 

Clayton L. Clem 

John Eric sen 

Karen Finstad 

Donald G. Heald 

Kathy Jones 

Settiana G. Kishnasamy 

Steve LaCasse 

Neal Lott 

Donald G. Marshall 

Nate Mulherin 

Alan B. Peabody, Chair 

Joe Pohlman 

Chuck Ryerson 

Tapani Seppa 

Longgang Shan 

Ronald M. Thorkildson 

H. B. White 



CONTENTS 



Page 

STANDARDS iii 

FOREWORD v 

ACKNOWLEDGMENTS vii 

Standard 

1.0 General 1 

1.1 Scope 1 

1.2 Definitions 1 

1.3 Basic Requirements 2 

1.3.1 Strength 2 

1.3.2 Serviceability 2 

1.3.3 Self- Straining Forces 2 

1.3.4 Analysis 2 

1.3.5 Counteracting Structural Actions 2 

1.4 General Structural Integrity 2 

1.5 Classification of Buildings and Other Structures 2 

1.5.1 Nature of Occupancy 2 

1.5.2 Hazardous Materials and Extremely Hazardous Materials 2 

1.6 Additions and Alterations to Existing Structures 3 

1.7 Load Tests 3 

2.0 Combinations of Loads 5 

2.1 General 5 

2.2 Symbols and Notation 5 

2.3 Combining Factored Loads Using Strength Design 5 

2.3.1 Applicability 5 

2.3.2 Basic Combinations 5 

2.3.3 Load Combinations Including Flood Load 5 

2.3.4 Load Combinations Including Atmospheric Ice Loads 5 

2.4 Combining Nominal Loads Using Allowable Stress Design 6 

2.4.1 Basic Combinations 6 

2.4.2 Load Combinations Including Flood Load 6 

2.4.3 Load Combinations Including Atmospheric Ice Loads 6 

2.5 Load Combinations for Extraordinary Events 6 

3.0 Dead Loads 7 

3.1 Definition 7 

3.2 Weights of Materials and Constructions 7 

3.3 Weight of Fixed Service Equipment 7 

4.0 Live Loads 9 

4.1 Definition 9 

4.2 Uniformly Distributed Loads 9 

4.2.1 Required Live Loads 9 

4.2.2 Provision for Partitions 9 

4.3 Concentrated Loads 9 

4.4 Loads on Handrails, Guardrail Systems, Grab Bar Systems, Vehicle Barrier Systems, 

and Fixed Ladders 9 



4.4.1 Definitions 9 

4.4.2 Loads 9 

4.5 Loads Not Specified 10 

4.6 Partial Loading 10 

4.7 Impact Loads 10 

4.7.1 Elevators 10 

4.7.2 Machinery 10 

4.8 Reduction in Live Loads 10 

4.8.1 General 10 

4.8.2 Heavy Live Loads 10 

4.8.3 Passenger Car Garages 11 

4.8.4 Special Occupancies 11 

4.8.5 Limitations on One- Way Slabs 11 

4.9 Minimum Roof Live Loads 11 

4.9.1 Flat, Pitched, and Curved Roofs 11 

4.9.2 Special-Purpose Roofs 11 

4.9.3 Special Structural Elements 11 

4. 10 Crane Loads 11 

4.10.1 Maximum Wheel Load 11 

4.10.2 Vertical Impact Force 1.1 

4.10.3 Lateral Force 11 

4.10.4 Longitudinal Force 12 

4.11 References 12 

5.0 Soil and Hydrostatic Pressure and Flood Loads 17 

5.1 Pressure on Basement Walls 17 

5.2 Uplift on Floors and Foundations 17 

5.3 Flood Loads 17 

5.3.1 Definitions 17 

5.3.2 Design Requirements 18 

5.3.2.1 Design Loads 18 

5.3.2.2 Erosion and Scour 18 

5.3.2.3 Loads on Breakaway Walls 18 

5.3.3 Loads During Flooding 18 

5.3.3.1 Load Basis 18 

5.3.3.2 Hydrostatic Loads 18 

5.3.3.3 Hydrodynamic Loads 18 

5.3.3.4 Wave Loads 18 

5.3.3.4.1 Breaking Wave Loads on Vertical Pilings and Columns 19 

5.3.3.4.2 Breaking Wave Loads on Vertical Walls 19 

5.3.3.4.3 Breaking Wave Loads on Nonvertical Walls 20 

5.3.3.4.4 Breaking Wave Loads from Obliquely Incident Waves 20 

5.3.3.5 Impact Loads 20 

5.4 Reference 20 

6.0 Wind Loads 23 

6.1 General 23 

6.1.1 Scope 23 

6.1.2 Allowed Procedures 23 

6.1.3 Wind Pressures Acting on Opposite Faces of Each Building Surface 23 

6.1.4 Minimum Design Wind Loading 23 

6.1.4.1 Main Wind Force-Resisting System 23 

6.1.4.2 Components and Cladding 23 

6.2 Definitions 23 



6.3 Symbols and Notations 25 

6.4 Method 1 — Simplified Procedure 26 

6.4.1 Scope 26 

6.4.1.1 Main Wind Force-Resisting Systems 26 

6.4.1.2 Components and Cladding 26 

6.4.2 Design Procedure 27 

6.4.2.1 Main Wind Force-Resisting System 27 

6.4.2.1.1 Minimum Pressures 27 

6.4.2.2 Components and Cladding 27 

6.4.2.2.1 Minimum Pressures 27 

6.4.3 Air-Permeable Cladding 27 

6.5 Method 2 — Analytical Procedure 27 

6.5.1 Scope 27 

6.5.2 Limitations 27 

6.5.2.1 Shielding 27 

6.5.2.2 Air-Permeable Cladding 27 

6.5.3 Design Procedure 28 

6.5.4 Basic Wind Speed 28 

6.5.4.1 Special Wind Regions 28 

6.5.4.2 Estimation of Basic Wind Speeds from Regional Climatic Data 28 

6.5.4.3 Limitation 28 

6.5.4.4 Wind Directionality Factor 28 

6.5.5 Importance Factor 28 

6.5.6 Exposure 28 

6.5.6.1 Wind Directions and Sectors 28 

6.5.6.2 Surface Roughness Categories 28 

6.5.6.3 Exposure Categories 29 

6.5.6.4 Exposure Category for Main Wind Force-Resisting Systems 29 

6.5.6.4.1 Buildings and Other Structures 29 

6.5.6.4.2 Low-Rise Buildings 29 

6.5.6.5 Exposure Category for Components and Cladding 29 

6.5.6.5.1 Buildings with Mean Roof Height h Less Than or Equal to 

60 ft (18 m) 29 

6.5.6.5.2 Buildings with Mean Roof Height h Greater Than 60 ft (18 m) 

and Other Structures 29 

6.5.6.6 Velocity Pressure Exposure Coefficient 29 

6.5.7 Topographic Effects 29 

6.5.7.1 Wind Speed-Up over Hills, Ridges, and Escarpments 29 

6.5.7.2 Topographic Factor 30 

6.5.8 Gust Effect Factor 30 

6.5.8.1 Rigid Structures 30 

6.5.8.2 Flexible or Dynamically Sensitive Structures 30 

6.5.8.3 Rational Analysis 30 

6.5.8.4 Limitations 30 

6.5.9 Enclosure Classifications 30 

6.5.9.1 General 30 

6.5.9.2 Openings 30 

6.5.9.3 Wind-Borne Debris 31 

6.5.9.4 Multiple Classifications 31 

6.5.10 Velocity Pressure 31 

6.5.11 Pressure and Force Coefficients 31 

6.5.11.1 Internal Pressure Coefficient 31 

6.5.11.1.1 Reduction Factor for Large Volume Buildings, /?/ 31 

6.5.11.2 External Pressure Coefficients 31 

6.5.11.2.1 Main Wind Force-Resisting Systems 31 



6.5 A 1. 22 Components and Cladding 31 

6.5.1.1.3 Force Coefficients 31 

6.5.11.4 Roof Overhangs 31 

6.5.11.4.1 Main Wind Force-Resisting System 31 

6.5.11.4.2 Components and Cladding 31 

6.5.11.5 Parapets 32 

6.5.11.5.1 Main Wind Force-Resisting System 32 

6.5.11.5.2 Components and Cladding 32 

6.5.12 Design Wind Loads on Enclosed and Partially Enclosed Buildings 32 

6.5.12.1 General 32 

6.5.12.1.1 Sign Convention 32 

6.5.12.1.2 Critical Load Condition 32 

6.5.12.1.3 Tributary Areas Greater Than 700 ft 2 (65 m 2 ) 32 

6.5.12.2 Main Wind Force-Resisting Systems 32 

6.5.12.2.1 Rigid Buildings of All Height 32 

6.5.12.2.2 Low-Rise Building 32 

6.5.12.2.3 Flexible Buildings 32 

6.5.12.2.4 Parapets 32 

6.5.12.3 Design Wind Load Cases 33 

6.5.12.4 Components and Cladding 33 

6.5.12.4.1 Low-Rise Buildings and Buildings with A < 60 ft (18.3 m) 33 

6.5.12.4.2 Buildings with h > 60 ft (18.3 m) 33 

6.5.12.4.3 Alternative Design Wind Pressures for Components 

and Cladding in Buildings with 60 ft (18.3 m) < h < 90 ft 

(27.4 m) 33 

6.5.12.4.4 Parapets 34 

6.5.13 Design Wind Loads on Open Buildings and Other Structures 34 

6.6 Method 3 — Wind-Tunnel Procedure 34 

6.6.1 Scope 34 

6.6.2 Test Conditions 34 

6.6.3 Dynamic Response 34 

6.6.4 Limitations 34 

6.6.4.1 Limitations on Wind Speeds 34 

6.7 References 35 

7.0 Snow Loads 77 

7.1 Symbols and Notations 77 

7.2 Ground Snow Loads, p g 77 

7.3 Flat Roof Snow Loads p f 77 

7.3.1 Exposure Factor, C e 77 

7.3.2 Thermal Factor, C t 77 

7.3.3 Importance Factor, / 77 

7.3.4 Minimum Values of pf for Low-Slope Roofs 77 

7.4 Sloped Roof Snow Loads, p s 77 

7.4.1 Warm Roof Slope Factor, C s 78 

7.4.2 Cold Roof Slope Factor, C s 78 

7.4.3 Roof Slope Factor for Curved Roofs 78 

7.4.4 Roof Slope Factor for Multiple Folded Plate, Sawtooth, and Barrel Vault Roofs 78 

7.4.5 Ice Dams and Icicles Along Eaves 78 

7.5 Partial Loading 78 

7.5.1 Continuous Beam Systems 78 

7.5.2 Other Structural Systems 78 

7.6 Unbalanced Roof Snow Loads 78 

7.6.1 Unbalanced Snow Loads for Hip and Gable Roofs 79 

7.6.2 Unbalanced Snow Loads for Curved Roofs 79 



7.6.3 Unbalanced Snow Loads for Multiple Folded Plate, Sawtooth, and Barrel Vault Roofs .... 79 

7.6.4 Unbalanced Snow Loads for Dome Roofs 79 

7.7 Drifts on Lower Roofs (Aerodynamic Shade) 79 

7.7.1 Lower Roof of a Structure 79 

7.7.2 Adjacent Structures and Terrain Features 80 

7.8 Roof Projections 80 

7.9 Sliding Snow 80 

7.10 Rain-on-Snow Surcharge Load 80 

7.1 1 Ponding Instability 80 

7.12 Existing Roofs 80 

8.0 Rain Loads 93 

8.1 Symbols and Notation 93 

8.2 Roof Drainage 93 

8.3 Design Rain Loads 93 

8.4 Ponding Instability 93 

8.5 Controlled Drainage 93 

9.0 Earthquake Loads 95 

9.1 General Provisions 95 

9.1.1 Purpose 95 

9.1.2 Scope and Application 95 

9.1.2.1 Scope 95 

9.1.2.3 Change of Use 95 

9.1.2.4 Application of Provisions 95 

9.1.2.4.1 New Buildings 95 

9.1.2.2 Additions to Existing Structures 96 

9.1.2.2.1 96 

9.1.2.2.2 96 

9.1.2.5 Alternate Materials and Methods of Construction 96 

9.1.3 Seismic Use Groups 96 

9.1.3.1 High Hazard Exposure Structures 96 

9.1.3.1.1 Seismic Use Group III Structure Protected Access 96 

9.1.3.1.2 Seismic Use Group III Function 96 

9.1.3.2 96 

9.1.3.3 96 

9.1.3.4 Multiple Use 96 

9.1.4 Occupancy Importance Factor 96 

9.2.1 Definitions 96 

9.2.2 Symbols 102 

9.3 107 

9.4.1 Procedures for Determining Maximum Considered Earthquake and Design Earthquake 

Ground Motion Accelerations and Response Spectra 107 

9.4.1.1 Maximum Considered Earthquake Ground Motions 107 

9.4.1.2 General Procedure for Determining Maximum Considered Earthquake and 

Design Spectral Response Accelerations 107 

9.4.1.2.1 Site Class Definitions 107 

9.4.1.2.2 Steps for Classifying a Site 128 

9.4.1.2.3 Definitions of Site Class Parameters 128 

9.4.1.2.4 Site Coefficients and Adjusted Maximum Considered Earthquake 
Spectral Response Acceleration Parameters 129 

9.4.1.2.5 Design Spectral Response Acceleration Parameters 129 

9.4.1.2.6 General Procedure Response Spectrum 129 

9.4.1.3 Site-Specific Procedure for Determining Ground Motion Accelerations 130 



9.4.1.3.1 Probabilistic Maximum Considered Earthquake 130 

9.4.1.3.2 Deterministic Limit on Maximum Considered Earthquake 

Ground Motion 131 

9.4.L3.3 Deterministic Maximum Considered Earthquake Ground Motion . . 131 

9.4.1.3.4 Site-Specific Design Ground Motion 131 

9.4.1.3.5 Design Acceleration Parameters 131 

9.4.2 Seismic Design Category 131 

9.4.2.1 Determination of Seismic Design Category 131 

9.4.2.2 Site Limitation for Seismic Design Categories E and F 131 

9.4.3 Quality Assurance 131 

9.5 Structural Design Criteria, Analysis, and Procedures 132 

9.5.1 This Section Has Been Intentionally Left Blank 132 

9.5.2 Structural Design Requirements 132 

9.5.2.1 Design Basis 132 

9.5.2.2 Basic Seismic Force-Resisting Systems 132 

9.5.2.2.1 Dual System 132 

9.5.2.2.2 Combinations of Framing Systems 132 

9.5.2.2.2.1 R and S2 Factors 136 

9.5.2.2.2.2 Combination Framing Detailing Requirements ... 136 

9.5.2.2.3 Seismic Design Categories B and C 136 

9.5.2.2.4 Seismic Design Categories D and E 136 

9.5.2.2.4.1 Increased Building Height Limit 136 

9.5.2.2.4.2 Interaction Effects 136 

9.5.2.2.4.3 Deformational Compatibility 136 

9.5.2.2.4.4 Special Moment Frames . 136 

9.5.2.2.5 Seismic Design Category F 137 

9.5.2.3 Structure Configuration 137 

9.5.2.3.1 Diaphragm Flexibility . 137 

9.5.2.3.2 Plan Irregularity 137 

9.5.2.3.3 Vertical Irregularity 137 

9.5.2.4 Redundancy 138 

9.5.2.4.1 Seismic Design Categories A, B, and C 138 

9.5.2.4.2 Seismic Design Category D 138 

9.5.2.4.3 Seismic Design Categories E and F 139 

9.5.2.5 Analysis Procedures 139 

9.5.2.5.1 Analysis Procedures 139 

9.5.2.5.2 Application of Loading 139 

9.5.2.5.2.1 Seismic Design Categories A and B 139 

9.5.2.5.2.2 Seismic Design Category C 139 

9.5.2.5.2.3 Seismic Design Categories D, E, and F 141 

9.5.2.6 Design and Detailing Requirements 141 

9.5.2.6.1 Seismic Design Category A 141 

9.5.2.6.1.1 Load Path Connections 141 

9.5.2.6.1.2 Anchorage of Concrete or Masonry Walls 141 

9.5.2.6.2 Seismic Design Category B 141 

9.5.2.6.2.1 P -Delta Effects 141 

9.5.2.6.2.2 Openings 141 

9.5.2.6.2.3 Direction of Seismic Load 141 

9.5.2.6.2.4 Discontinuities in Vertical System 141 

9.5.2.6.2.5 Nonredundant Systems 142 

9.5.2.6.2.6 Collector Elements 142 

9.5.2.6.2.7 Diaphragms 142 

9.5.2.6.2.8 Anchorage of Concrete or Masonry Walls 142 

9.5.2.6.2.9 Inverted Pendulum-Type Structures 142 

9.5.2.6.2.10 Anchorage of Nonstructural Systems 142 



9.5.2.6.2.11 Elements Supporting Discontinuous Walls 

or Frames 142 

9.5.2.6.3 Seismic Design Category C 143 

9.5.2.6.3.1 Collector Elements 143 

9.5.2.6.3.2 Anchorage of Concrete or Masonry Walls 143 

9.5.2.6.4 Seismic Design Category D 143 

9.5.2.6.4.1 Collector Elements 143 

9.5.2.6.4.2 Plan or Vertical Irregularities 144 

9.5.2.6.4.3 Vertical Seismic Forces 144 

9.5.2.6.4.4 Diaphragms 144 

9.5.2.6.5 Seismic Design Categories E and F 144 

9.5.2.6.5.1 Plan or Vertical Irregularities 144 

9.5.2.7 Combination of Load Effects 144 

9.5.2.7.1 Special Seismic Load 145 

9.5.2.8 Deflection, Drift Limits, and Building Separation 145 

9.5.3 Index Force Analysis Procedure for Seismic Design of Buildings 145 

9.5.4 Simplified Analysis Procedure for Seismic Design of Buildings 146 

9.5.4.1 Seismic Base Shear 146 

9.5.4.2 Vertical Distribution 146 

9.5.4.3 Horizontal Distribution 146 

9.5.4.4 Design Drift 146 

9.5.5 Equivalent Lateral Force Procedure 146 

9.5.5.1 General 146 

9.5.5.2 Seismic Base Shear 146 

9.5.5.2.1 Calculation of Seismic Response Coefficient 146 

9.5.5.3 Period Determination 147 

9.5.5.3.1 Upper Limit on Calculated Period 147 

9.5.5.3.2 Approximate Fundamental Period 147 

9.5.5.4 Vertical Distribution of Seismic Forces 148 

9.5.5.5 Horizontal Shear Distribution and Torsion 148 

9.5.5.5.1 Direct Shear 148 

9.5.5.5.2 Torsion 148 

9.5.5.6 Overturning 148 

9.5.5.7 Drift Determination and P -Delta Effects 149 

9.5.5.7.1 Story Drift Determination 149 

9.5.5.7.2 /> -Delta Effects 149 

9.5.6 Modal Analysis Procedure 150 

9.5.6.1 General 150 

9.5.6.2 Modeling 150 

9.5.6.3 Modes 150 

9.5.6.4 Periods 150 

9.5.6.5 Modal Base Shear 150 

9.5.6.6 Modal Forces, Deflections, and Drifts 151 

9.5.6.7 Modal Story Shears and Moments 151 

9.5.6.8 Design Values 151 

9.5.6.9 Horizontal Shear Distribution 152 

9.5.6.10 Foundation Overturning 152 

9.5.6.11 P -Delta Effects 152 

9.5.7 Linear Response History Analysis Procedure 152 

9.5.7.1 Modeling 152 

9.5.7.2 Ground Motion 152 

9.5.7.2.1 Two-Dimensional Analysis 152 

9.5.7.2.2 Three-Dimensional Analysis 152 

9.5.7.3 Response Parameters 152 

9.5.8 Nonlinear Response History Analysis 153 



9.5.8.1 Modeling 153 

9.5.8.2 Ground Motion and Other Loading 153 

9.5.8.3 Response Parameters 153 

9.5.8.3.1 Member Strength 153 

9.5.8.3.2 Member Deformation 153 

9.5.8.3.3 Interstory Drift 1 54 

9.5.8.4 Design Review 154 

9.5.9 Soil-Structure Interaction 154 

9.5.9.1 General 154 

9.5.9.2 Equivalent Lateral Force Procedure 154 

9.5.9.2.1 Base Shear 154 

9.5.9.2.1.1 Effective Building Period 154 

9.5.9.2.1.2 Effective Damping 155 

9.5.9.2.2 Vertical Distribution of Seismic Forces 156 

9.5.9.2.3 Other Effects 156 

9.5.9.3 Modal Analysis Procedure 156 

9.5.9.3.1 Modal Base Shears 156 

9.5.9.3.2 Other Modal Effects 157 

9.5.9.3.3 Design Values 157 

9.6 Architectural, Mechanical, and Electrical Components and Systems 157 

9.6.1 General 157 

9.6.1.1 Reference Standards 158 

9.6.1.1.1 Consensus Standards 158 

9.6.1.1.2 Accepted Standards 159 

9.6.1.2 Component Force Transfer 159 

9.6.1.3 Seismic Forces 159 

9.6.1.4 Seismic Relative Displacements 160 

9.6.1.5 Component Importance Factor 160 

9.6.1.6 Component Anchorage 160 

9.6.1.6.1 160 

9.6.1.6.2 160 

9.6.1.6.3 161 

9.6.1.6.4 161 

9.6.1.6.5 161 

9.6.1.6.6 161 

9.6.1.7 Construction Documents 161 

9.6.2 Architectural Component Design 161 

9.6.2.1 General 161 

9.6.2.2 Architectural Component Forces and Displacements 161 

9.6.2.3 Architectural Component Deformation 161 

9.6.2.4 Exterior Nonstructural Wall Elements and Connections 162 

9.6.2.4.1 General 162 

9.6.2.4.2 Glass 163 

9.6.2.5 Out-of-Plane Bending 163 

9.6.2.6 Suspended Ceilings 163 

9.6.2.6.1 Seismic Forces 163 

9.6.2.6.2 Industry Standard Construction 163 

9.6.2.6.2.1 Seismic Design Category C 163 

9.6.2.6.2.2 Seismic Design Categories D, E, and F 163 

9.6.2.6.3 Integral Ceiling/Sprinkler Construction 164 

9.6.2.7 Access Floors 164 

9.6.2.7.1 General 164 

9.6.2.7.2 Special Access Floors 164 

9.6.2.8 Partitions 164 

9.6.2.8.1 General 164 



9.6.2.8.2 Glass 164 

9.6.2.9 Steel Storage Racks 164 

9.6.2.10 Glass in Glazed Curtain Walls, Glazed Storefronts, and Glazed Partitions .... 165 

9.6.2.10.1 General 165 

9.6.2.10.2 Seismic Drift Limits for Glass Components 165 

9.6.3 Mechanical and Electrical Component Design 165 

9.6.3.1 General 165 

9.6.3.2 Mechanical and Electrical Component Forces and Displacements 165 

9.6.3.3 Mechanical and Electrical Component Period 165 

9.6.3.4 Mechanical and Electrical Component Attachments 166 

9.6.3.5 Component Supports 167 

9.6.3.6 Component Certification 167 

9.6.3.7 Utility and Service Lines at Structure Interfaces 167 

9.6.3.8 Site-Specific Considerations . 167 

9.6.3.9 Storage Tanks Mounted in Structures 167 

9.6.3.10 HVAC Ductwork 167 

9.6.3.11 Piping Systems 168 

9.6.3.11.1 Pressure Piping Systems 168 

9.6.3.11.2 Fire Protection Sprinkler Systems 168 

9.6.3.11.3 Other Piping Systems 168 

9.6.3.11.4 Supports and Attachments for Other Piping 168 

9.6.3.12 Boilers and Pressure Vessels 169 

9.6.3.12.1 ASME Boilers and Pressure Vessels 169 

9.6.3.12.2 Other Boilers and Pressure Vessels . 169 

9.6.3.12.3 Supports and Attachments for Other Boilers and Pressure Vessels . 169 

9.6.3.13 Mechanical Equipment, Attachments, and Supports 169 

9.6.3.13.1 Mechanical Equipment 170 

9.6.3.13.2 Attachments and Supports for Mechanical Equipment 170 

9.6.3.14 Electrical Equipment, Attachments, and Supports 170 

9.6.3.14.1 Electrical Equipment 170 

9.6.3.14.2 Attachments and Supports for Electrical Equipment 171 

9.6.3.15 Alternative Seismic Qualification Methods 171 

9.6.3.16 Elevator Design Requirements 171 

9.6.3.16.1 Reference Document 171 

9.6.3.16.2 Elevators and Hoistway Structural System 172 

9.6.3.16.3 Elevator Machinery and Controller Supports and Attachments .... 172 

9.6.3.16.4 Seismic Controls 172 

9.6.3.16.5 Retainer Plates 172 

9.7 Foundation Design Requirements 172 

9.7.1 General 172 

9.7.2 Seismic Design Category A 172 

9.7.3 Seismic Design Category B 172 

9.7.3.1 Structural Components 172 

9.7.3.2 Soil Capacities 172 

9.7.4 Seismic Design Category C 172 

9.7.4.1 Investigation 172 

9.7.4.2 Pole-Type Structures 173 

9.7.4.3 Foundation Ties 173 

9.7.4.4 Special Pile Requirements 173 

9.7.5 Foundation Requirements for Seismic Design Categories D, E, and F 173 

9.7.5.1 Investigation 173 

9.7.5.2 Foundation Ties 173 

9.7.5.3 Liquefaction Potential and Soil Strength Loss 173 

9.7.5.4 Special Pile and Grade Beam Requirements 173 

9.8 Steel 174 



9.8.1 Reference Documents 174 

9.9 Structural Concrete 174 

9.9.1 Reference Documents 174 

9.10 Composite Structures 174 

9.10.1 Reference Documents 174 

9.10.1.1 175 

9.11 Masonry 175 

9.11.1 Reference Documents 175 

9.12 Wood 175 

9.12.1 Reference Documents 175 

9.12.1.1 Consensus Standards 175 

9.12.1.2 Other References 175 

9.1.3 Provisions for Seismically Isolated Structures 175 

9.13.1 General 175 

9.13.2 Criteria Selection 175 

9.13.2.1 Basis for Design 175 

9.13.2.2 Stability of the Isolation System . 175 

9.13.2.3 Seismic Use Group 176 

9.13.2.4 Configuration Requirements 176 

9.13.2.5 Selection of Lateral Response Procedure 176 

9.13.2.5.1 General . 176 

9.13.2.5.2 Equivalent Lateral Force Procedure 176 

9.13.2.5.3 Dynamic Analysis 176 

9.13.2.5.3.1 Response-Spectrum Analysis 176 

9.13.2.5.3.2 Time-History Analysis 176 

9.13.2.5.3.3 Site-Specific Design Spectra 176 

9.13.3 Equivalent Lateral Force Procedure 176 

9.13.3.1 General 176 

9.13.3.2 Deformation Characteristics of the Isolation System 176 

9.13.3.3 Minimum Lateral Displacements 177 

9.13.3.3.1 Design Displacement 177 

9.13.3.3.2 Effective Period at Design Displacement 177 

9.13.3.3.3 Maximum Lateral Displacement 177 

9.13.3.3.4 Effective Period at Maximum Displacement 177 

9.13.3.3.5 Total Lateral Displacement 178 

9.13.3.4 Minimum Lateral Forces 178 

9.13.3.4.1 Isolation System and Structural Elements at or Below the 

Isolation System 178 

9.13.3.4.2 Structural Elements Above the Isolation System 178 

9.13.3.4.3 Limits on V s 179 

9.13.3.5 Vertical Distribution of Force 179 

9.13.3.6 Drift Limits 179 

9.13.4 Dynamic Lateral Response Procedure 179 

9.13.4.1 General 179 

9.13.4.2 Isolation System and Structural Elements Below the Isolation System 179 

9.13.4.3 Structural Elements Above the Isolation System 180 

9.13.4.4 Ground Motion 180 

9.13.4.4.1 Design Spectra 180 

9.13.4.4.2 Time Histories 180 

9.13.4.5 Mathematical Model 180 

9.13.4.5.1 General 180 

9.13.4.5.2 Isolation System 180 

9.13.4.5.3 Isolated Building 181 

9.13.4.5.3.1 Displacement 181 

9.13.4.5.3.2 Forces and Displacements in Key Elements 181 



9.13.4.6 Description of Analysis Procedures 181 

9.13.4.6.1 General 181 

9.13.4.6.2 Input Earthquake 181 

9.13.4.6.3 Response-Spectrum Analysis 181 

9.13.4.6.4 Time-History Analysis 181 

9.13.4.7 Design Lateral Force 181 

9.13.4.7.1 Isolation System and Structural Elements at or Below the 

Isolation System . . 181 

9.13.4.7.2 Structural Elements Above the Isolation System 181 

9.13.4.7.3 Scaling of Results 181 

9.13.4.7.4 Drift Limits 182 

9.13.5 Lateral Load on Elements of Structures and Nonstructural Components Supported 

by Buildings 182 

9.13.5.1 General 182 

9.13.5.2 Forces and Displacements . 182 

9.13.5.2.1 Components at or Above the Isolation Interface 182 

9.13.5.2.2 Components Crossing the Isolation Interface 182 

9.13.5.2.3 Components Below the Isolation Interface 182 

9.13.6 Detailed System Requirements 182 

9.13.6.1 General 182 

9.13.6.2 Isolation System 182 

9.13.6.2.1 Environmental Conditions 182 

9.13.6.2.2 Wind Forces 182 

9.13.6.2.3 Fire Resistance 182 

9.13.6.2.4 Lateral Restoring Force 182 

9.13.6.2.5 Displacement Restraint 183 

9.13.6.2.6 Vertical-Load Stability 183 

9.13.6.2.7 Overturning 183 

9.13.6.2.8 Inspection and Replacement 183 

9.13.6.2.9 Quality Control 183 

9.13.6.3 Structural System 183 

9.13.6.3.1 Horizontal Distribution of Force 183 

9.13.6.3.2 Building Separations 183 

9.13.6.3.3 Nonbuilding Structures 183 

9.13.7 Foundations 183 

9.13.8 Design and Construction Review 184 

9.13.8.1 General 184 

9.13.8.2 Isolation System 184 

9.13.9 Required Tests of the Isolation System 184 

9.13.9.1 General 184 

9.13.9.2 Prototype Tests 184 

9.13.9.2.1 General 184 

9.13.9.2.2 Record 184 

9.13.9.2.3 Sequence and Cycles 184 

9.13.9.2.4 Units Dependent on Loading Rates 184 

9.13.9.2.5 Units Dependent on Bilateral Load 185 

9.13.9.2.6 Maximum and Minimum Vertical Load 185 

9.13.9.2.7 Sacrificial Wind-Restraint Systems 185 

9.13.9.2.8 Testing Similar Units 185 

9.13.9.3 Determination of Force-Deflection Characteristics 185 

9.13.9.4 System Adequacy 185 

9.13.9.5 Design Properties of the Isolation System 185 

9.13.9.5.1 Maximum and Minimum Effective Stiffness 185 

9.13.9.5.2 Effective Damping 186 

9.14 Nonbuilding Structures 186 



9.14.1 General 186 

9.14.1.1 Nonbuilding Structures 186 

9.14.1.2 Design 186 

9.14.2 Reference Standards 187 

9.14.2.1 Consensus Standards 187 

9.14.2.2 Accepted Standards 187 

9.14.3 Industry Design Standards and Recommended Practice 188 

9.14.4 Nonbuilding Structures Supported by Other Structures 188 

9.14.4.1 Architectural, Mechanical, and Electrical Components 188 

9.14.5 Structural Design Requirements 188 

9.14.5.1 Design Basis 188 

9.14.5.1.1 Seismic Factors 191 

9.14.5.1.2 Importance Factors and Seismic Use Group Classifications 191 

9.14.5.2 Rigid Nonbuilding Structures 192 

9.14.5.3 Loads 192 

9.14.5.4 Fundamental Period 192 

9.14.5.5 Drift Limitations 192 

9.14.5.6 Materials Requirements 192 

9.14.5.7 Deflection Limits and Structure Separation 192 

9.14.5.8 Site-Specific Response Spectra 192 

9.14.6 Nonbuilding Structures Similar to Buildings 192 

9.14.6.1 General 192 

9.14.6.2 Pipe Racks 193 

9.14.6.2.1 Design Basis 193 

9.14.6.3 Steel Storage Racks 193 

9.14.6.3.1 General Requirements 193 

9.14.6.3.2 Operating Weight 193 

9.14.6.3.3 Vertical Distribution of Seismic Forces 193 

9.14.6.3.4 Seismic Displacements 193 

9.14.6.4 Electrical Power Generating Facilities 194 

9.14.6.4.1 General 194 

9.14.6.4.2 Design Basis 194 

9.14.6.5 Structural Towers for Tanks and Vessels 194 

9.14.6.5.1 General 194 

9.14.6.6 Piers and Wharves 194 

9.14.6.6.1 General 194 

9.14.6.6.2 Design Basis 194 

9.14.7 Nonbuilding Structures Not Similar to Buildings 194 

9.14.7.1 General 194 

9.14.7.2 Earth-Retaining Structures 194 

9.14.7.2.1 General 194 

9.14.7.3 Tanks and Vessels 194 

9.14.7.3.1 General 194 

9.14.7.3.2 Design Basis 195 

9.14.7.3.3 Strength and Ductility 195 

9.14.7.3.4 Flexibility of Piping Attachments 195 

9.14.7.3.5 Anchorage 196 

9.14.7.3.6 Ground-Supported Storage Tanks for Liquids 196 

9.14.7.3.6.1 General 196 

9.14.7.3.6.1.1 Distribution of Hydrodynamic and 
Inertia Forces 197 

9.14.7.3.6.1.2 Freeboard 197 

9.14.7.3.6.1.3 Equipment and Attached Piping . 197 

9.14.7.3.6.1.4 Internal Components 198 

9.14.7.3.6.1.5 Sliding Resistance 198 



9.14.7.3.6.1.6 Local Shear Transfer 198 

9.14.7.3.6.1.7 Pressure Stability 199 

9.14.7.3.6.1.8 Shell Support 199 

9.14.7.3.6.1.9 Repair, Alteration, or 
Reconstruction 199 

9.14.7.3.7 Water and Water Treatment Tanks and Vessels 199 

9.14.7.3.7.1 Welded Steel 199 

9.14.7.3.7.2 Bolted Steel 199 

9.14.7.3.7.3 Reinforced and Prestressed Concrete 200 

9.14.7.3.8 Petrochemical and Industrial Tanks and Vessels Storing Liquids . . 200 

9.14.7.3.8.1 Welded Steel 200 

9.14.7.3.8.2 Bolted Steel 200 

9.14.7.3.8.3 Reinforced and Prestressed Concrete 200 

9.14.7.3.9 Ground-Supported Storage Tanks for Granular Materials 200 

9.14.7.3.9.1 General 200 

9.14.7.3.9.2 Lateral Force Determination 200 

9.14.7.3.9.3 Force Distribution to Shell and Foundation 201 

9.14.7.3.9.3.1 Increased Lateral Pressure 201 

9.14.7.3.9.3.2 Effective Mass 201 

9.14.7.3.9.3.3 Effective Density 201 

9.14.7.3.9.3.4 Lateral Sliding 201 

9.14.7.3.9.3.5 Combined Anchorage Systems . . 201 

9.14.7.3.9.4 Welded Steel Structures 201 

9.14.7.3.9.5 Bolted Steel Structures 201 

9.14.7.3.9.6 Reinforced Concrete Structures 201 

9.14.7.3.9.7 Prestressed Concrete Structures 201 

9.14.7.3.10 Elevated Tanks and Vessels for Liquids and Granular Materials . . . 201 

9.14.7.3.10.1 General 201 

9.14.7.3.10.2 Effective Mass 201 

9.14.7.3.10.3 P -Delta Effects 202 

9.14.7.3.10.4 Transfer of Lateral Forces into Support Tower ... 202 

9.14.7.3.10.5 Evaluation 

of Structures Sensitive to Buckling Failure 202 

9.14.7.3.10.6 Welded Steel Water Storage Structures 202 

9.14.7.3.10.6.1 Analysis Procedures 203 

9.14.7.3.10.6.2 Structure Period 203 

9.14.7.3.10.7 Concrete Pedestal (Composite) Tanks 203 

9.14.7.3.10.7.1 Analysis Procedures 203 

9.14.7.3.10.7.2 Structure Period 203 

9.14.7.3.11 Boilers and Pressure Vessels 203 

9.14.7.3.11.1 General 203 

9.14.7.3.11.2 ASME Boilers and Pressure Vessels 203 

9.14.7.3.11.3 Attachments of Internal Equipment and 

Refractory 203 

9.14.7.3.11.4 Coupling of Vessel and Support Structure 204 

9.14.7.3.11.5 Effective Mass 204 

9.14.7.3.11.6 Other Boilers and Pressure Vessels 204 

9.14.7.3.11.7 Supports and Attachments for Boilers and 

Pressure Vessels 204 

9.14.7.3.12 Liquid and Gas Spheres 204 

9.14.7.3.12.1 General 204 

9.14.7.3.12.2 ASME Spheres 204 

9.14.7.3.12.3 Attachments of Internal Equipment and 

Refractory 205 

9.14.7.3.12.4 Effective Mass 205 



9.14.73.12.5 Post and Rod Supported 205 

9.14.7,3.12.6 Skirt Supported 205 

9.14.7.3.13 Refrigerated Gas Liquid Storage Tanks and Vessels 205 

9.14.7.3.13.1 General 205 

9.14.7.3.14 Horizontal, Saddle- Supported Vessels for Liquid or 

Vapor Storage 205 

9.14.7.3.14.1 General 205 

9.14.7.3.14.2 Effective Mass 205 

9.14.7.3.14.3 Vessel Design 205 

9.14.7.4 Stacks and Chimneys 206 

9.14.7.4.1 General 206 

9.14.7.4.2 Design Basis 206 

9.14.7.5 Amusement Structures 206 

9.14.7.5.1 General 206 

9.14.7.5.2 Design Basis 206 

9.14.7.6 Special Hydraulic Structures 206 

9.14.7.6.1 General 206 

9.14.7.6.2 Design Basis 206 

9.14.7.7 Secondary Containment Systems 206 

9.14.7.7.2 Freeboard 206 

9.14.7.8 Telecommunication Towers 206 

10.0 Ice Loads — Atmospheric Icing 207 

10.1 General 207 

10.1.1 Site-Specific Studies 207 

10.1.2 Dynamic Loads 207 

10.1.3 Exclusions 207 

10.2 Definitions 207 

10.3 Symbols and Notation 207 

10.4 Ice Loads Due to Freezing Rain 208 

10.4.1 Ice Weight 208 

10.4.2 Nominal Ice Thickness 208 

10.4.3 Height Factor 208 

10.4.4 Importance Factors 208 

10.4.5 Topographic Factor 208 

10.4.6 Design Ice Thickness for Freezing Rain 208 

10.5 Wind on Ice-Covered Structures 208 

10.5.1 Wind on Ice-Covered Chimneys, Tanks, and Similar Structures 209 

10.5.2 Wind on Ice-Covered Solid Freestanding Walls and Solid Signs 209 

10.5.3 Wind on Ice-Covered Open Signs and Lattice Frameworks 209 

10.5.4 Wind on Ice-Covered Trussed Towers 209 

10.6 Partial Loading 209 

10.7 Design Procedure 209 

10.8 References 209 

Appendix A 

A. 9 Supplemental Provisions 217 

A.9.1 Purpose 217 

A.9.3 Quality Assurance 217 

A.9.3.1 Scope 217 

A.9.3.2 Quality Assurance Plan 217 

A.9.3.2.1 Details of Quality Assurance Plan 217 

A.9.3.2.2 Contractor Responsibility 218 

A.9.3. 3 Special Inspection 218 



A.9.3.3.1 Foundations 218 

A.9.3.3.2 Reinforcing Steel 218 

A.9.3.3.2.1 218 

A.9.3.3.2.2 218 

A.9.3.3.3 Structural Concrete 218 

A.9.3.3.4 Prestressed Concrete 218 

A.9.3.3.5 Structural Masonry 218 

A.9.3.3.5.1 218 

A.9.3.3.5.2 218 

A.9.3.3.6 Structural Steel . 218 

A.9.3.3.6.1 ... 218 

A.9.3.3.6.2 218 

A.9.3.3.7 Structural Wood 218 

A.9.3.3.7.1 218 

A.9.3.3.7.2 219 

A.9.3.3.7.3 218 

A.9.3.3.8 Cold-Formed Steel Framing 219 

A.9.3.3.8.1 219 

A.9.3.3.8.2 219 

A.9.3.3.9 Architectural Components 219 

A.9.3.3.10 Mechanical and Electrical Components 219 

A.9.3.3.11 Seismic Isolation System 219 

A.9.3.4 Testing 219 

A. 9. 3.4.1 Reinforcing and Prestressing Steel 219 

A.9.3A1.1 219 

A.9.3A1.2 219 

A.9.3A1.3 219 

A.9.3A2 Structural Concrete 220 

A.9.3A3 Structural Masonry 220 

A.9.3A4 Structural Steel 220 

A.9.3.4A1 Base Metal Testing 220 

A.9.3.4. 5 Mechanical and Electrical Equipment 220 

A.9.3.4.6 Seismic-Isolated Structures 220 

A.9.3.5 Structural Observations 220 

A. 9. 3. 6 Reporting and Compliance Procedures 220 

A.9.7 Supplementary Foundation Requirements 220 

A.9.7A4 Special Pile Requirements for Category C 220 

A.9.7 A4.1 Uncased Concrete Piles 221 

A.9.7.4A2 Metal-Cased Concrete Piles 221 

A.9.7 A4.3 Concrete-Filled Pipe 221 

A.9.7 A4.4 Precast Nonprestressed Concrete Piles 221 

A.9.7 A4.5 Precast Prestressed Piles 221 

A.9.7.5 Special Pile Requirements for Categories D, E, and F 221 

A.9.7.5A1 Uncased Concrete Piles 221 

A.9.7.5 A2 Metal-Cased Concrete Piles 222 

A.9.7.5 A3 Precast Concrete Piles 222 

A.9.7.5 A4 Precast Prestressed Piles 222 

A.9.7.5 A5 Steel Piles 223 

A.9.8 Supplementary Provisions for Steel 223 

A.9.8.1 General 223 

A.9.8. 2 Seismic Requirements for Steel Structures 223 

A.9.8.3 Seismic Design Categories A, B, and C 223 

A.9.8.4 Seismic Design Categories D, E, and F 223 

A.9.8. 5 Cold-Formed Steel Seismic Requirements 223 

A.9.8.5.1 223 



A. 9. 8.6 Light-Framed Wall Requirements 223 

A.9.8.6.1 Boundary Members 223 

A.9.8.6.2 Connections 223 

A.9.8.6.3 Braced Bay Members 223 

A.9.8.6.4 Diagonal Braces 224 

A.9.8.6.5 Shear Walls 224 

A.9.8.7 Seismic Requirements for Steel Deck Diaphragms 224 

A.9.8.8 Steel Cables 224 

A. 9. 9 Supplemental Provisions for Concrete 224 

A.9.9.1 Modifications to Ref. 9.9-1 (ACI 318-02) 224 

A.9.9.1. 1 ACI 318, Section 21.0 224 

A.9.9.1.2 ACI 318, Section 21.1 224 

A.9.9.1. 3 ACI 318, Section 21.2.5 224 

A.9.9.1.4 ACI 318, Section 21.7 225 

A.9.9.1.5 ACI 318, Section 21.10 225 

A.9.9.1.6 ACI 318, Section 21.11 225 

A.9.9.1.7 ACI 318 Section D.4.2 225 

A.9.9.2 Classification of Shear Walls 225 

A.9.9.2.1 Ordinary Plain Concrete Shear Walls 225 

A.9.9.2.2 Detailed Plain Concrete Shear Walls 225 

A.9.9.2.3 Ordinary Reinforced Concrete Shear Walls 226 

A.9.9.2.4 Special Reinforced Concrete Shear Walls 226 

A.9.9.3 Seismic Design Category B 226 

A.9.9.3.1 Ordinary Moment Frames 226 

A. 9. 9.4 Seismic Design Category C 226 

A. 9. 9.4.1 Seismic Force-Resisting Systems 226 

A.9.9.4.2 Discontinuous Members 226 

A.9.9.4.3 Anchor Bolts in the Top of Columns 226 

A.9.9.4.4 Plain Concrete 226 

A.9.9.4.4.1 Walls 226 

A.9.9.4A2 Footings 226 

A.9.9.4.4.3 Pedestals 227 

A. 9. 9. 5 Seismic Design Categories D, E, and F 227 

A. 9. 9. 5.1 Seismic Force-Resisting Systems 227 

A.9.9.5.2 Frame Members Not Proportioned to Resist Forces Induced by 

Earthquake Motions 227 

A.9.11 Supplementary Provisions for Masonry 227 

A.9.11.1 227 

A.9.11.2 227 

A.9.11.3 227 

A.9.1 1.4 227 

A.9.11.4.1 Method A 227 

A.9.1 1.4.2 Method B 228 

A.9.11.5 228 

Appendix B 

B.O Serviceability Considerations 229 

B.l Deflection, Vibration, and Drift 229 

B.l.l Vertical Deflections 229 

B.1.2 Drift of Walls and Frames 229 

B.1.3 Vibrations 229 

B.2 Design for Long-Term Deflection 229 

B.3 Camber 229 

B.4 Expansion and Contraction 229 

B.5 Durability . . . 229 



Commentary 

C1.0 General 232 

Cl.l Scope 232 

CI. 3 Basic Requirements 232 

Cl.3.1 Strength 232 

Cl.3.2 Serviceability 232 

Cl.3.3 Self-Straining Forces 232 

C1.4 General Structural Integrity 232 

CI. 5 Classification of Buildings and Other Structures 235 

CI. 5.1 Nature of Occupancy 235 

CI. 5. 2 Hazardous Materials and Extremely Hazardous Materials 236 

C1.7 Load Tests 236 

References 237 

C2.0 Combinations of Loads 239 

C2.2 Symbols and Notation 239 

C2.3 Combining Loads Using Strength Design 239 

C2.3.1 Applicability 239 

C2.3.2 Basic Combinations 239 

C2.3.3 Load Combinations Including Flood Load 240 

C2.3.4 Load Combinations Including Atmospheric Ice Loads . . 241 

C2.4 Combining Loads Using Allowable Stress Design 241 

C2.4.1 Basic Combinations 241 

C2.4.2 Load Combinations Including Flood Load 241 

C2.4.3 Load Combinations Including Atmospheric Ice Loads 241 

C2.5 Load Combinations for Extraordinary Events 242 

References 243 

C3.0 Dead Loads 245 

C3.2 Weights of Materials and Constructions 245 

C4.0 Live Loads 254 

C4.2 Uniformly Distributed Loads 254 

C4.2.1 Required Live Loads 254 

C4.3 Concentrated Loads 255 

C4.3.1 Accessible Roof- Supporting Members 255 

C4.4 Loads on Handrails, Guardrail Systems, Grab Bar Systems, and Vehicle Barrier Systems 255 

C4.4.2 Loads 255 

C4.6 Partial Loading 255 

C4.7 Impact Loads 255 

C4.8 Reduction in Live Loads 255 

C4.8.1 General 255 

C4.8.2 Heavy Live Loads 256 

C4.8.3 Parking Garage Loads 256 

C4.8.5 Limitations on One- Way Slabs 256 

C4.9 Minimum Roof Live Loads 256 

C4.9.1 Flat, Pitched, and Curved Roofs 256 

C4.9.2 Special Purpose Roofs 256 

C4.10 Crane Loads . 257 

References 257 

C5.0 Soil and Hydrostatic Pressure and Flood Loads 261 

C5.1 Pressure on Basement Walls 261 

C5.2 Uplift on Floors and Foundations 261 



C5.3 Flood Loads 261 

C5.3.1 Definitions 261 

C5.3.2 Design Requirements 262 

C5.3.2.1 Design Loads 262 

C5.3.2.2 Erosion and Scour 262 

C5.3.3.6 Loads on Breakaway Walls 262 

C5.3.3.1 Load Basis 263 

C5.3.3.2 Hydrostatic Loads 263 

C5.3.3.3 Hydrodynamic Loads 263 

C5.3.3.4 Wave Loads 263 

C5.3.3.4.2 Breaking Wave Loads on Vertical Walls 264 

C5.3.3.5 Impact Loads 264 

References 267 

C6.0 Wind Loads 271 

C6.1 General 271 

C6.2 Definitions 271 

C6.3 Symbols and Notation 272 

C6.4 Method 1 — Simplified Procedure 273 

C6.5 Method 2 — Analytical Procedure 273 

C6.5.1 Scope 273 

C6.5.2 Limitations of Analytical Procedure 274 

C6.5.2.1 Shielding 274 

C6.5.2.2 Air-Permeable Cladding 274 

C6.5.4 Basic Wind Speed 274 

C6.5.4.1 Special Wind Regions 276 

C6.5.4.2 Estimation of Basic Wind Speeds from Regional Climatic Data 276 

C6.5.4.3 Limitation 276 

C6.5.4.4 Wind Directionality Factor 276 

C6.5.5 Importance Factor 277 

C6.5.6 Exposure Categories 277 

C6.5.6.4 Velocity Pressure Exposure Coefficient 282 

C6.5.7 Wind Speed-Up over Hills and Escarpments 283 

C6.5.8 Gust Effect Factors 283 

C6.5.9 Enclosure Classifications 284 

C6.5.10 Velocity Pressure 285 

C6.5.11 Pressure and Force Coefficients 286 

C6.5.11.1 Internal Pressure Coefficients 290 

C6.5.1 1.5 Parapets 290 

C6.5.12 Design Wind Loads on Buildings 291 

C6.5.12.3 Design Wind Load Cases 291 

C6.6 Method 3 — Wind-Tunnel Procedure 292 

References 293 

C7.0 Snow Loads 313 

C7.2 Ground Snow Loads 313 

C7.3 Flat Roof Snow Loads, p f 315 

C7.3.1 Exposure Factor, C e 315 

C7.3.2 Thermal Factor, C t 316 

C7.3.3 Importance Factor, / 317 

C7.3.4 Minimum Allowable Values of pf for Low-Slope Roofs 317 

C7.4 Sloped Roof Snow Loads, p s 317 

C7.4.3 Roof Slope Factor for Curved Roofs 318 

C7.4.4 Roof Slope Factor for Multiple Folded Plate, Sawtooth, and Barrel Vault Roofs 318 



C7.4.5 Ice Dams and Icicles Along Eaves 318 

C7.5 Unloaded Portions 318 

C7.6 Unbalanced Roof Snow Loads 318 

C7.6.1 Unbalanced Snow Loads on Hip and Gable Roofs 318 

C7.6.2 Unbalanced Snow Loads for Curved Roofs 318 

C7.6.3 Unbalanced Snow Loads for Multiple Folded Plate, Sawtooth, and Barrel 

Vault Roofs 319 

C7.6.4 Unbalanced Snow Loads for Dome Roofs 319 

C7.7 Drifts on Lower Roofs (Aerodynamic Shade) 319 

C7.8 Roof Projections 320 

C7.9 Sliding Snow 320 

C7.10 Rain-on-Snow Surcharge Load 320 

C7.ll Ponding Instability 321 

C7.12 Existing Roofs 321 

C7.13 Other Roofs and Sites 321 

References 324 

C8.0 Rain Loads 335 

C8.1 Symbols and Notation 335 

C8.2 Roof Drainage 335 

C8.3 Design Rain Loads 335 

C8.4 Ponding Instability 335 

C8.5 Controlled Drainage 336 

References 336 

C9.0 Earthquake Loads 339 

C9.1.1 Purpose 341 

C9.4.1.1 Maximum Considered Earthquake Ground Motions 341 

C9.5.2.4 Redundancy 341 

C9.5.2.5.1 Seismic Design Category A 342 

C9.5.2.6.2.5 Nonredundant Systems 342 

C9. 5. 2. 6.2. 11 Elements Supporting Discontinuous 

Walls or Frames 342 

C9. 5. 2.6. 2. 8 Anchorage of Concrete or Masonry 

Walls 342 

C9.5.2.7.1 Special Seismic Loads 342 

C9.5.5.5.5 Torsion 342 

C9.5.4.3 Horizontal Distribution 343 

C9.5.9 Soil Structure Interaction 343 

C9.6.1.4 Seismic Relative Displacements 343 

C9.6.2.10 Glass in Glazed Curtain Walls, Glazed Storefronts, and Glazed 

Partitions 343 

C9.7.4.1 Investigation 343 

C9.7.5 Foundation Requirements for Seismic Design Categories D, E, and F 343 

C9.7.5.3 Liquefaction Potential and Soil Strength Loss 343 

C9.7.5.4 Special Pile and Grade Beam Requirements 344 

C9.9 Structural Concrete 344 

C9.12 Wood 344 

C9.14 Nonbuilding Structures 344 

C9.14.2 Reference Standards 344 

C9.14.3 Industry Design Standards and Recommended Practice 344 

C9.14.7.3 Tanks and Vessels 345 

C9. 14.7.3.6. 1.4 Internal Components .... 345 

C9.14.7.3.8.2 Bolted Steel 345 



C9. 14.7.7 Secondary Containment Systems 345 

C9. 14.7.8 Telecommunication Towers 345 

CA.9.7.4.4.1 Uncased Concrete Piles 345 

CA. 9. 7.4.4.4 Precast Nonprestressed Concrete Piles 346 

CA.9.7 .4.4.5 Precast Prestressed Piles 346 

CA.9.7.5.4.1 Uncased Concrete Piles 346 

CA.9.7.5.4.3 Precast Concrete Piles 346 

CA.9.7.5.4.4 Precast-Prestressed Piles 346 

CA.9.9 Supplementary Provisions for Concrete 346 

CA.9.11 Supplementary Provisions for Masonry 346 

C10.0 Ice Loads — Atmospheric Icing 351 

C10.1 General 351 

C10.1.1 Site-Specific Studies 351 

C10.1.2 Dynamic Loads 352 

CIO. 1.3 Exclusions 352 

C10.2 Definitions 352 

C10.4 Ice Loads Due to Freezing Rain 353 

C10.4.1 Ice Weight 353 

C10.4.2 Nominal Ice Thickness 353 

C10.4.4 Importance Factors 355 

C 10.4.6 Design Ice Thickness for Freezing Rain 355 

C10.5 Wind-on-Ice-Covered Structures 356 

C10.6 Partial Loading 356 

References 356 

CB Serviceability Considerations 365 

CB.1.1 Vertical Deflections and Misalignment 365 

CB.1.2 Drift of Walls and Frames 366 

CB.1.3 Vibrations 366 

CB.2 Design for Long-Term Deflection 367 

CB.3 Camber 367 

CB.4 Expansion and Contraction 367 

CB.5 Durability 367 

References 367 

Index 369 



SECTION 1.0 

GENERAL 



SECTION 1.1 
SCOPE 

This standard provides minimum load requirements for the 
design of buildings and other structures that are subject 
to building code requirements. Loads and appropriate load 
combinations, which have been developed to be used 
together, are set forth for strength design and allowable 
stress design. For design strengths and allowable stress 
limits, design specifications for conventional structural 
materials used in buildings and modifications contained in 
this standard shall be followed. 



SECTION 1.2 

DEFINITIONS 

The following definitions apply to the provisions of the 
entire standard. 

ALLOWABLE STRESS DESIGN. A method of propor- 
tioning structural members such that elastically computed 
stresses produced in the members by nominal loads do not 
exceed specified allowable stresses (also called working 
stress design). 

AUTHORITY HAVING JURISDICTION. The organi- 
zation, political subdivision, office, or individual charged 
with the responsibility of administering and enforcing the 
provisions of this standard. 

BUILDINGS. Structures, usually enclosed by walls and 
a roof, constructed to provide support or shelter for an 
intended occupancy. 

DESIGN STRENGTH. The product of the nominal 
strength and a resistance factor. 

ESSENTIAL FACILITIES. Buildings and other struc- 
tures that are intended to remain operational in the event of 
extreme environmental loading from wind, snow, or earth- 
quakes. 

FACTORED LOAD. The product of the nominal load and 
a load factor. 

HAZARDOUS MATERIAL. Chemicals or substances 
classified as a physical or health hazard whether the chem- 
icals or substances are in a usable or waste condition. 

HEALTH HAZARD. Chemicals or substances classified 
by the authority having jurisdiction as toxic, highly toxic, 
or corrosive. 



LIMIT STATE. A condition beyond which a structure or 
member becomes unfit for service and is judged either to 
be no longer useful for its intended function (serviceability 
limit state) or to be unsafe (strength limit state). 

LOAD EFFECTS. Forces and deformations produced in 
structural members by the applied loads. 

LOAD FACTOR. A factor that accounts for deviations of 
the actual load from the nominal load, for uncertainties in 
the analysis that transforms the load into a load effect, and 
for the probability that more than one extreme load will 
occur simultaneously. 

LOADS. Forces or other actions that result from the 
weight of all building materials, occupants and their pos- 
sessions, environmental effects, differential movement, and 
restrained dimensional changes. Permanent loads are those 
loads in which variations over time are rare or of small 
magnitude. All other loads are variable loads, (see also 
nominal loads.) 

NOMINAL LOADS. The magnitudes of the loads speci- 
fied in Sections 3 through 9 (dead, live, soil, wind, snow, 
rain, flood, and earthquake) of this standard. 

NOMINAL STRENGTH. The capacity of a structure 
or member to resist the effects of loads, as determined 
by computations using specified material strengths and 
dimensions and formulas derived from accepted principles 
of structural mechanics or by field tests or laboratory 
tests of scaled models, allowing for modeling effects and 
differences between laboratory and field conditions. 

OCCUPANCY. The purpose for which a building or other 
structure, or part thereof, is used or intended to be used. 

OTHER STRUCTURES. Structures, other than build- 
ings, for which loads are specified in this standard. 

P-DELTA EFFECT. The second-order effect on shears 
and moments of frame members induced by axial loads 
on a laterally displaced building frame. 

PHYSICAL HAZARD. Chemicals or substances in a liq- 
uid, solid, or gaseous form that are classified by the 
authority having jurisdiction as combustible, flammable, 
explosive, oxidizer, pyrophoric, unstable (reactive), or 
water reactive. 

RESISTANCE FACTOR. A factor that accounts for devi- 
ations of the actual strength from the nominal strength and 



Minimum Design Loads for Buildings and Other Structures 



the manner and consequences of failure (also called strength 
reduction factor), 

STRENGTH DESIGN. A method of proportioning struc- 
tural members such that the computed forces produced 
in the members by the factored loads do not exceed the 
member design strength (also called load and resistance 
factor design). 

TEMPORARY FACILITIES. Buildings or other struc- 
tures that are to be in service for a limited time and have a 
limited exposure period for environmental loadings. 



SECTION 1.3 
BASIC REQUIREMENTS 

1.3.1 Strength. Buildings and other structures, and all 
parts thereof, shall be designed and constructed to support 
safely the factored loads in load combinations defined in 
this document without exceeding the appropriate strength 
limit states for the materials of construction. Alternatively, 
buildings and other structures, and all parts thereof, shall 
be designed and constructed to support safely the nominal 
loads in load combinations defined in this document without 
exceeding the appropriate specified allowable stresses for 
the materials of construction. 

1.3.2 Serviceability. Structural systems, and members 
thereof, shall be designed to have adequate stiffness to 
limit deflections, lateral drift, vibration, or any other 
deformations that adversely affect the intended use and 
performance of buildings and other structures. 

1.3.3 Self-Straining Forces. Provision shall be made for 
anticipated self- straining forces arising from differential 
settlements of foundations and from restrained dimensional 
changes due to temperature, moisture, shrinkage, creep, and 
similar effects. 

1.3.4 Analysis. Load effects on individual structural mem- 
bers shall be determined by methods of structural analysis 
that take into account equilibrium, general stability, geo- 
metric compatibility, and both short- and long-term material 
properties. Members that tend to accumulate residual defor- 
mations under repeated service loads shall have included 
in their analysis the added eccentricities expected to occur 
during their service life. 

1.3.5 Counteracting Structural Actions. All structural 
members and systems, and all components and cladding 
in a building or other structure, shall be designed to resist 
forces due to earthquake and wind, with consideration 
of overturning, sliding, and uplift, and continuous load 
paths shall be provided for transmitting these forces to the 
foundation. Where sliding is used to isolate the elements, 



the effects of friction between sliding elements shall be 
included as a force. Where all or a portion of the resistance 
to these forces is provided by dead load, the dead load 
shall be taken as the minimum dead load likely to be 
in place during the event causing the considered forces. 
Consideration shall be given to the effects of vertical and 
horizontal deflections resulting from such forces. 



SECTION 1.4 
GENERAL STRUCTURAL INTEGRITY 

Buildings and other structures shall be designed to sustain 
local damage with the structural system as a whole remain- 
ing stable and not being damaged to an extent dispropor- 
tionate to the original local damage. This shall be achieved 
through an arrangement of the structural elements that pro- 
vides stability to the entire structural system by transfer- 
ring loads from any locally damaged region to adjacent 
regions capable of resisting those loads without collapse. 
This shall be accomplished by providing sufficient continu- 
ity, redundancy, or energy-dissipating capacity (ductility), 
or a combination thereof, in the members of the structure. 



SECTION 1.5 

CLASSIFICATION OF BUILDINGS AND OTHER 

STRUCTURES 

1.5.1 Nature of Occupancy. Buildings and other struc- 
tures shall be classified, based on the nature of occupancy, 
according to Table 1-1 for the purposes of applying flood, 
wind, snow, earthquake, and ice provisions. The categories 
range from I to IV, where Category I represents buildings 
and other structures with a low hazard to human life in the 
event of failure and Category IV represents essential facil- 
ities. Each building or other structure shall be assigned to 
the highest applicable category or categories. Assignment 
of the same structure to multiple categories based on use 
and the type of load condition being evaluated (e.g., wind, 
seismic, etc.) shall be permissible. 

When buildings or other structures have multiple uses 
(occupancies), the relationship between the uses of various 
parts of the building or other structure and the independence 
of the structural systems for those various parts shall be 
examined. The classification for each independent structural 
system of a multiple use building or other structure shall 
be that of the highest usage group in any part of the 
building or other structure that is dependent on that basic 
structural system. 

1.5.2 Hazardous Materials and Extremely Hazardous 
Materials. Buildings and other structures containing haz- 
ardous materials or extremely hazardous materials are per- 
mitted to be classified as Category II structures if it can 
be demonstrated to the satisfaction of the authority having 
jurisdiction by a hazard assessment as part of an overall 



ASCE 7-02 



risk management plan (RMP) that a release of the haz- 
ardous material or extremely hazardous material does not 
pose a threat to the public. 

In order to qualify for this reduced classification, the 
owner or operator of the buildings or other structures 
containing the hazardous materials or extremely haz- 
ardous materials shall have a risk management plan 
that incorporates three elements as a minimum: a haz- 
ard assessment, a prevention program, and an emergency 
response plan. 

As a minimum, the hazard assessment shall include the 
preparation and reporting of worst-case release scenarios for 
each structure under consideration, showing the potential 
effect on the public for each. As a minimum, the worst- 
case event shall include the complete failure (instantaneous 
release of entire contents) of a vessel, piping system, or 
other storage structure. A worst-case event includes (but 
is not limited to) a release during the design wind or 
design seismic event. In this assessment, the evaluation 
of the effectiveness of subsequent measures for accident 
mitigation shall be based on the assumption that the 
complete failure of the primary storage structure has 
occurred. The off-site impact must be defined in terms of 
population within the potentially affected area. In order to 
qualify for the reduced classification, the hazard assessment 
shall demonstrate that a release of the hazardous material 
from a worst-case event does not pose a threat to the public 
outside the property boundary of the facility. 

As a minimum, the prevention program shall consist 
of the comprehensive elements of process safety man- 
agement, which is based on accident prevention through 
the application of management controls in the key areas 
of design, construction, operation, and maintenance. Sec- 
ondary containment of the hazardous materials or extremely 
hazardous materials (including, but not limited to, double 
wall tank, dike of sufficient size to contain a spill, or other 
means to contain a release of the hazardous materials or 
extremely hazardous material within the property bound- 
ary of the facility and prevent release of harmful quantities 



of contaminants to the air, soil, ground water, or surface 
water) are permitted to be used to mitigate the risk of 
release. When secondary containment is provided, it shall 
be designed for all environmental loads and is not eligible 
for this reduced classification. In hurricane-prone regions, 
mandatory practices and procedures that effectively dimin- 
ish the effects of wind on critical structural elements or that 
alternatively protect against harmful releases during and 
after hurricanes may be used to mitigate the risk of release. 
As a minimum, the emergency response plan shall 
address public notification, emergency medical treatment 
for accidental exposure to humans, and procedures for 
emergency response to releases that have consequences 
beyond the property boundary of the facility. The emer- 
gency response plan shall address the potential that 
resources for response could be compromised by the event 
that has caused the emergency. 

SECTION 1.6 

ADDITIONS AND ALTERATIONS TO EXISTING 

STRUCTURES 

When an existing building or other structure is enlarged 
or otherwise altered, structural members affected shall be 
strengthened if necessary so that the factored loads defined 
in this document will be supported without exceeding 
the specified design strength for the materials of con- 
struction. When using allowable stress design, strength- 
ening is required when the stresses due to nominal loads 
exceed the specified allowable stresses for the materials of 
construction. 

SECTION 1.7 
LOAD TESTS 

A load test of any construction shall be conducted when 
required by the authority having jurisdiction whenever there 
is reason to question its safety for the intended occupancy 
or use. 



Minimum Design Loads for Buildings and Other Structures 



TABLE 1-1 
CLASSIFICATION OF BUILDINGS AND OTHER STRUCTURES FOR FLOOD, WIND, SNOW, EARTHQUAKE, AND ICE LOADS 



Nature of Occupancy 


Category 


Buildings and other structures that represent a low hazard to human life in the event of failure including, 
but not limited to: 

Agricultural facilities 

Certain temporary facilities 

Minor storage facilities 


I 


All buildings and other structures except those listed in Categories I, III, and IV 


II 


Buildings and other structures that represent a substantial hazard to human life in the event of failure 

including, but not limited to: 

Buildings and other structures where more than 300 people congregate in one area 

Buildings and other structures with day care facilities with capacity greater than 150 

Buildings and other structures with elementary school or secondary school facilities with capacity 

greater than 250 

Buildings and other structures with a capacity greater than 500 for colleges or adult education facilities 

Health care facilities with a capacity of 50 or more resident patients but not having surgery or 

emergency treatment facilities 

Jails and detention facilities 

Power generating stations and other public utility facilities not included in Category IV 

Buildings and other structures not included in Category IV (including, but not limited to, facilities that 
manufacture, process, handle, store, use, or dispose of such substances as hazardous fuels, hazardous 
chemicals, hazardous waste, or explosives) containing sufficient quantities of hazardous materials to be 
dangerous to the public if released. 

Buildings and other structures containing hazardous materials shall be eligible for classification as Category 
II structures if it can be demonstrated to the satisfaction of the authority having jurisdiction by a hazard 
assessment as described in Section 1.5.2 that a release of the hazardous material does not pose a threat to 
the public. 


III 


Buildings and other structures designated as essential facilities including, but not limited to: 
Hospitals and other health care facilities having surgery or emergency treatment facilities 
Fire, rescue, ambulance, and police stations and emergency vehicle garages 
Designated earthquake, hurricane, or other emergency shelters 
Designated emergency preparedness, communication, and operation centers and other facilities required 

for emergency response 
Power generating stations and other public utility facilities required in an emergency 
Ancillary structures (including, but not limited to, communication towers, fuel storage tanks, cooling 

towers, electrical substation structures, fire water storage tanks or other structures housing or 

supporting water, or other fire-suppression material or equipment) required for operation of Category 

IV structures during an emergency 
Aviation control towers, air traffic control centers, and emergency aircraft hangars 
Water storage facilities and pump structures required to maintain water pressure for fire suppression 
Buildings and other structures having critical national defense functions 

Buildings and other structures (including, but not limited to, facilities that manufacture, process, handle, 
store, use, or dispose of such substances as hazardous fuels, hazardous chemicals, hazardous waste, or 
explosives) containing extremely hazardous materials where the quantity of the material exceeds a 
threshold quantity established by the authority having jurisdiction. 

Buildings and other structures containing extremely hazardous materials shall be eligible for classification 
as Category II structures if it can be demonstrated to the satisfaction of the authority having jurisdiction by 
a hazard assessment as described in Section 1.5.2 that a release of the extremely hazardous material does 
not pose a threat to the public. This reduced classification shall not be permitted if the buildings or other 
structures also function as essential facilities. 


IV 



ASCE 7-02 



SECTION 2,0 

COMBINATIONS OF LOADS 



SECTION 2.1 
GENERAL 

Buildings and other structures shall be designed using the 
provisions of either Section 2.3 or 2.4. Either Section 2.3 or 
2.4 shall be used exclusively for proportioning elements of 
a particular construction material throughout the structure. 



SECTION 2,2 
SYMBOLS AND NOTATION 

D = dead load; 

Dj = weight of ice; 

E — earthquake load; 

F = load due to fluids with well-defined pressures and 

maximum heights; 
F a — flood load; 
H = load due to lateral earth pressure, ground water 

pressure, or pressure of bulk materials; 
L — live load; 
L r = roof live load; 
R = rain load; 
S = snow load; 
T == self- straining force; 
W = wind load; 
W( — wind-on-ice determined in accordance with 

Section 10. 



SECTION 2.3 

COMBINING FACTORED LOADS USING 

STRENGTH DESIGN 

2.3.1 Applicability. The load combinations and load fac- 
tors given in Section 2.3.2 shall be used only in those cases 
in which they are specifically authorized by the applicable 
material design standard. 

2.3.2 Basic Combinations. Structures, components, and 
foundations shall be designed so that their design strength 
equals or exceeds the effects of the factored loads in the 
following combinations: 

1. 1.4(D + F) 

2. 1.2(D + F + T) + 1.6(L + H) + 0.5(L r or S or R) 

3. 1.2D + 1.6(L, or S or R) + (L or 0.8 W) 

4. 1.2D + 1.6W + L + 0.5(L r or S or R) 

5. 1.2D+1.0E + L+0.2S 



6. 0.9D + 1.6W + 1.6// 

7. G.9D + L0£ + 1.6# 

Exceptions: 

1. The load factor on L in combinations (3), (4), and 
(5) is permitted to equal 0.5 for all occupancies 
in which L in Table 4.1 is less than or equal to 
100 psf, with the exception of garages or areas 
occupied as places of public assembly. 

2. The load factor on H shall be set equal to 
zero in combinations (6) and (7) if the structural 
action due to H counteracts that due to W ox E. 
Where lateral earth pressure provides resistance 
to structural actions from other forces, it shall 
not be included in H but shall be included in the 
design resistance. 

Each relevant strength limit state shall be investigated. 
Effects of one or more loads not acting shall be investigated. 
The most unfavorable effects from both wind and earth- 
quake loads shall be investigated, where appropriate, but 
they need not be considered to act simultaneously. Refer to 
Section 9.2.2 for specific definition of the earthquake load 
effect E} 

2.3.3 Load Combinations Including Flood Load. When 
a structure is located in a flood zone (Section 5.3.1), the 
following load combinations shall be considered: 

1. In V-Zones or Coastal A-Zones, 1.6 W in combina- 
tions (4) and (6) shall be replaced by 1.6W + 2.0iv 

2. In noncoastal A~Zones, 1.6W in combinations (4) and 
(6) shall be replaced by 0.8 W + l.0F a . 

23.4 Load Combinations Including Atmospheric Ice 
Loads. When a structure is subjected to atmospheric ice 
and wind-on-ice loads, the following load combinations 
shall be considered: 

1. 0.5 (L r or S or R) in combination (2) shall be 
replaced by 0.2 A + 0.5 S. 

2. \.6W + 0.5 (L r or S or R) in combination (4) shall 
be replaced by D t + W t + 0.53. 

3. 1.6W in combination (6) shall be replaced by 
D { + W h 



1 The same E from Section 9 is used for both Section 2.3.2 
and Section 2.4.1. Refer to the Commentary for Section 9. 



Minimum Design Loads for Buildings and Other Structures 



SECTION 2.4 

COMBINING NOMINAL LOADS USING 

ALLOWABLE STRESS DESIGN 

2.4.1 Basic Combinations. Loads listed herein shall be 
considered to act in the following combinations; whichever 
produces the most unfavorable effect in the building, 
foundation, or structural member being considered. Effects 
of one or more loads not acting shall be considered. 



D+ F 
D+H+F+L+T 

D + H + F + (L r or S or R) 

D + H + F + 0J5(L + T) + 0.75(L r or S or R) 

D + H + F + (W or OJE) 

D + H + F + 0.75( W or OJE) + 0J5L + 0J5(L r 
or S or R) 

Q.6D + W + H 

0.6D + 0.7£ + H 



The most unfavorable effects from both wind and 
earthquake loads shall be considered, where appropriate, 
but they need not be assumed to act simultaneously. Refer 
to Section 9.2.2 for the specific definition of the earthquake 
load effect E? 

Increases in allowable stress shall not be used with the 
loads or load combinations given in this standard unless it 
can be demonstrated that such an increase is justified by 
structural behavior caused by rate or duration of load. 



2 The same E from Section 9 is used for both Section 2.3.2 
and Section 2.4.1. Refer to the Commentary for Section 9. 



2.4.2 Load Combinations Including Flood Load. When 
a structure is located in a flood zone, the following load 
combinations shall be considered: 

1. In V-Zones or Coastal A-Zones (Section 5.3.1), 
\5F a shall be added to other loads in combinations 
(5), (6), and (7) and E shall be set equal to zero in 
(5) and (6). 

2. In noncoastal A-Zones, QJ5F a shall be added to 
combinations (5), (6), and (7) and E shall be set equal 
to zero in (5) and (6). 

2.4.3 Load Combinations Including Atmospheric Ice 
Loads. When a structure is subjected to atmospheric ice 
and wind-on-ice loads, the following load combinations 
shall be considered: 

1. OJDi shall be added to combination (2). 

2. (L r or S or R) in combination (3) shall be replaced 
by OJDj + OJWj + S. 

3. W in combination (7) shall be replaced by 0.7D,- + 

0.7 W;. 



SECTION 2.5 
LOAD COMBINATIONS FOR 
EXTRAORDINARY EVENTS 

Where required by the applicable code, standard, or the 
authority having jurisdiction, strength and stability shall be 
checked to ensure that structures are capable of withstand- 
ing the effects of extraordinary (i.e., low-probability) events 
such as fires, explosions, and vehicular impact. 



ASCE 7-02 



SECTION 3.0. 

DEAD LOADS 



SECTION 3.1 

DEFINITION 

Dead loads consist of the weight of all materials of 
construction incorporated into the building including but 
not limited to walls, floors, roofs, ceilings, stairways, 
built-in partitions, finishes, cladding and other similarly 
incorporated architectural and structural items, and fixed 
service equipment including the weight of cranes. 



SECTION 3.2 

WEIGHTS OF MATERIALS AND 

CONSTRUCTIONS 

In determining dead loads for purposes of design, the 
actual weights of materials and constructions shall be 



used provided that in the absence of definite information, 
values approved by the authority having jurisdiction shall 
be used. 



SECTION 3.3 
WEIGHT OF FIXED SERVICE EQUIPMENT 

In determining dead loads for purposes of design, the 
weight of fixed service equipment such as plumbing stacks 
and risers, electrical feeders, and heating, ventilating, and 
air conditioning systems shall be included. 



Minimum Design Loads for Buildings and Other Structures 



SECTION 4.0 

LIVE LOADS 



SECTION 4.1 
DEFINITION 

Live loads are those loads produced by the use and occu- 
pancy of the building or other structure and do not include 
construction or environmental loads such as wind load, 
snow load, rain load, earthquake load, flood load, or dead 
load. Live loads on a roof are those produced (1) during 
maintenance by workers, equipment, and materials, and 
(2) during the life of the structure by movable objects such 
as planters and by people. 



SECTION 4.2 
UNIFORMLY DISTRIBUTED LOADS 

4.2.1 Required Live Loads. The live loads used in the 
design of buildings and other structures shall be the 
maximum loads expected by the intended use or occupancy 
but shall in no case be less than the minimum uniformly 
distributed unit loads required by Table 4-1. 

4.2.2 Provision for Partitions. In office buildings or other 
buildings where partitions will be erected or rearranged, 
provision for partition weight shall be made, whether or 
not partitions are shown on the plans, unless the specified 
live load exceeds 80 lb/ft 2 (3.83 kN/m 2 ). 



SECTION 4.3 
CONCENTRATED LOADS 

Floors and other similar surfaces shall be designed to sup- 
port safely the uniformly distributed live loads prescribed 
in Section 4.2 or the concentrated load, in pounds or kilo- 
newtons (kN), given in Table 4-1, whichever produces 
the greater load effects. Unless otherwise specified, the 
indicated concentration shall be assumed to be uniformly 
distributed over an area 2.5 ft square (762 mm square) 
[6.25 ft 2 (0.58 m 2 )] and shall be located so as to produce 
the maximum load effects in the structural members. 

Any single panel point of the lower chord of exposed 
roof trusses or any point along the primary structural 
members supporting roofs over manufacturing, commercial 
storage and warehousing, and commercial garage floors 
shall be capable of carrying safely a suspended concentrated 
load of not less than 2000 lb (pound-force) (8.90 kN) 
in addition to dead load. For all other occupancies, a 
load of 200 lb (0.89 kN) shall be used instead of 2000 lb 
(8.90 kN). 



SECTION 4.4 

LOADS ON HANDRAILS, GUARDRAIL 

SYSTEMS, GRAB BAR SYSTEMS, VEHICLE 

BARRIER SYSTEMS, AND FIXED LADDERS 

4.4.1 Definitions. 

HANDRAIL. A rail grasped by hand for guidance and 
support. A handrail assembly includes the handrail, sup- 
porting attachments, and structures. 

FIXED LADDER. A ladder that is permanently attached 
to a structure, building, or equipment. 

GUARDRAIL SYSTEM. A system of building compo- 
nents near open sides of an elevated surface for the purpose 
of minimizing the possibility of a fall from the elevated 
surface by people, equipment, or material. 

GRAB BAR SYSTEM. A bar provided to support body 
weight in locations such as toilets, showers, and tub 
enclosures. 

VEHICLE BARRIER SYSTEM. A system of building 
components near open sides of a garage floor or ramp, or 
building walls that act as restraints for vehicles. 

4.4.2 Loads. 

(a) Handrail assemblies and guardrail systems shall be 
designed to resist a load of 50 lb/ft (pound-force per 
linear ft) (0.73 kN/m) applied in any direction at the 
top and to transfer this load through the supports to 
the structure. For one- and two-family dwellings, the 
minimum load shall be 20 lb/ft (0.29 kN/m). 
Further, all handrail assemblies and guardrail sys- 
tems shall be able to resist a single concentrated 
load of 200 lb (0.89 kN) applied in any direction 
at any point along the top, and have attachment 
devices and supporting structure to transfer this 
loading to appropriate structural elements of the 
building. This load need not be assumed to act 
concurrently with the loads specified in the preceding 
paragraph. 

Intermediate rails (all those except the handrail), 
balusters, and panel fillers shall be designed to with- 
stand a horizontally applied normal load of 50 lb 
(0.22 kN) on an area not to exceed 1 ft 2 (305 mm 2 ) 
including openings and space between rails. Reac- 
tions due to this loading are not required to be super- 
imposed with those of either preceding paragraph. 



Minimum Design Loads for Buildings and Other Structures 



(b) Grab bar systems shall be designed to resist a single 
concentrated load of 250 lb (1.1 1 kN) applied in any 
direction at any point. 

(c) Vehicle barrier systems for passenger cars shall 
be designed to resist a single load of 6000 lb 
(26.70 kN) applied horizontally in any direction to 
the barrier system, and shall have anchorages or 
attachments capable of transferring this load to the 
structure. For design of the system, the load shall 
be assumed to act at a minimum height of 1 ft, 
6 in. (460 mm) above the floor or ramp surface 
on an area not to exceed 1 ft 2 (305 mm 2 ), and 
is not required to be assumed to act concurrently 
with any handrail or guardrail loadings specified in 
the preceding paragraphs of Section 4.4.2. Garages 
accommodating trucks and buses shall be designed 
in accordance with an approved method, which 
contains provision for traffic railings. 

(d) The minimum design live load on fixed ladders 
with rungs shall be a single concentrated load of 
300 lbs, and shall be applied at any point to produce 
the maximum load effect on the element being 
considered. The number and position of additional 
concentrated live load units shall be a minimum of 
1 unit of 300 lbs for every 10 ft of ladder height. 

(e) Where rails of fixed ladders extend above a floor 
or platform at the top of the ladder, each side rail 
extension shall be designed to resist a concentrated 
live load of 100 lbs in any direction at any height up 
to the top of the side rail extension. Ship ladders with 
treads instead of rungs shall have minimum design 
loads as stairs, defined in Table 4-1. 

SECTION 4.5 

LOADS NOT SPECIFIED 

For occupancies or uses not designated in Section 4.2. or 
4,3, the live load shall be determined in accordance with a 
method approved by the authority having jurisdiction. 

SECTION 4.6 
PARTIAL LOADING 

The full intensity of the appropriately reduced live load 
applied only to a portion of a structure or member shall 
be accounted for if it produces a more unfavorable effect 
than the same intensity applied over the full structure 
or member. 

SECTION 4 J 

IMPACT LOADS 

The live loads specified in Sections 4.2.1 and 4.4.2 shall 
be assumed to include adequate allowance for ordinary 
impact conditions. Provision shall be made in the structural 



design for uses and loads that involve unusual vibration and 
impact forces. 

4.7.1 Elevators. All elevator loads shall be increased by 
100% for impact and the structural supports shall be 
designed within the limits of deflection prescribed by 
Refs. 4-1 and 4-2. 

4.7.2 Machinery. For the purpose of design, the weight of 
machinery and moving loads shall be increased as follows 
to allow for impact: 

(1) elevator machinery, 100%; 

(2) light machinery, shaft- or motor-driven, 20%; 

(3) reciprocating machinery or power-driven units, 50%; 

(4) hangers for floors or balconies, 33%. All percent- 
ages shall be increased where specified by the 
manufacturer. 



SECTION 4.8 
REDUCTION IN LIVE LOADS 

The minimum uniformly distributed live loads, L in 
Table 4-1, may be reduced according to the following 
provisions. 

4.8.1 General. Subject to the limitations of Sections 4.8.2 
through 4.8.5, members for which a value of KllAt is 
400 ft 2 (37.16 m 2 ) or more are permitted to be designed 
for a reduced live load in accordance with the following 
formula: 



L = L J 0.25 + 



15 



JkUAt 



(Eq. 4-1) 



In SI: 



where 



L = L \ 0.25 + 



4.57 



s/^llAi 



L — reduced design live load per square ft (m) of area 

supported by the member 
L G — unreduced design live load per square ft (m) of 
area supported by the member (see Table 4-1) 
K LL = live load element factor (see Table 4-2) 
A T — tributary area in ft 2 (m 2 ) 

L shall not be less than 0.50L o for members supporting 
one floor and L shall not be less than 0.401^ for members 
supporting two or more floors. 

4.8.2 Heavy Live Loads. Live loads that exceed 100 lb/ft 2 
(4.79 kN/m 2 ) shall not be reduced except the live loads 
for members supporting two or more floors may be 
reduced by 20%. 



10 



ASCE 7-02 



4.8.3 Passenger Car Garages. The live loads shall not 
be reduced in passenger car garages except the live loads 
for members supporting two or more floors may be 
reduced by 20%. 



where, for a pitched roof, F = number of inches of rise 
per ft (in SI: F — 0.12 x slope, with slope expressed in 
percentage points) and, for an arch or dome, F = rise-to- 
span ratio multiplied by 32. 



4.8.4 Special Occupancies. Live loads of 100 lbs/ft 2 
(4.79 kN/m 2 ) or less shall not be reduced in public 
assembly occupancies. 

4.8.5 Limitations on One-Way Slabs. The tributary area, 
At, for one-way slabs shall not exceed an area defined by 
the slab span times a width normal to the span of 1 .5 times 
the slab span. 



SECTION 4,9 
MINIMUM ROOF LIVE LOADS 

4.9.1 Flat, Pitched, and Curved Roofs. Ordinary flat, 
pitched, and curved roofs shall be designed for the live 
loads specified in Eq. 4-2 or other controlling combina- 
tions of loads as discussed in Section 2, whichever pro- 
duces the greater load. In structures such as greenhouses, 
where special scaffolding is used as a work surface for 
workmen and materials during maintenance and repair 
operations, a lower roof load than specified in Eq. 4-2 
shall not be used unless approved by the authority having 
jurisdiction. 

L r = 20RiR 2 where 12 < L r < 20 (Eq. 4-2) 

in SI: L r = 0.96/?ifl 2 where 0.58 < L r < 0.96 

where L r — roof live load/ft 2 of horizontal projection 
in lbs/ ft 2 (kN/m 2 ). 

The reduction factors R\ and R2 shall be determined 
as follows: 

1 for A t < 200 ft 2 (18.58 m 2 ) 

R\ = 1.2 - 0.001 A t for 200 ft 2 < A t < 600 ft 2 
0.6 for A, > 600 ft 2 (55. 74 m 2 ) 

in SI: 

1 for A t < 18.58 m 2 

#1 = 1.2 - 0.01076A f for 18.58 m 2 < A t < 55.74 m 2 
0.6 for A t > 55.74 m 2 

where A t = tributary area in ft 2 (m 2 ) supported by any 
structural member and 



1 



for F < 4 



R7 = 1.2 - 0.05 F for 4 < F < 12 



0.6 



for F > 12 



4.9.2 Special-Purpose Roofs. Roofs used for promenade 
purposes shall be designed for a minimum live load of 
60 lb/ft 2 (2.87 kN/m 2 ). Roofs used for roof gardens or 
assembly purposes shall be designed for a minimum live 
load of 100 lb/ft 2 (4.79 kN/m 2 ). Roofs used for other 
special purposes shall be designed for appropriate loads 
as approved by the authority having jurisdiction. 

4.9.3 Special Structural Elements. Live loads of 100 lbs/ 
ft 2 (4.79 kN/m 2 ) or less shall not be reduced for roof 
members except as specified in 4.9. 



SECTION 4.10 
CRANE LOADS 

The crane live load shall be the rated capacity of the crane. 
Design loads for the runway beams, including connections 
and support brackets, of moving bridge cranes and monorail 
cranes shall include the maximum wheel loads of the crane 
and the vertical impact, lateral, and longitudinal forces 
induced by the moving crane. 

4.10.1 Maximum Wheel Load. The maximum wheel 
loads shall be the wheel loads produced by the weight of 
the bridge, as applicable, plus the sum of the rated capacity 
and the weight of the trolley with the trolley positioned on 
its runway at the location where the resulting load effect 
is maximum. 

4.10.2 Vertical Impact Force. The maximum wheel loads 
of the crane shall be increased by the percentages shown 
below to determine the induced vertical impact or vibration 
force: 

Monorail cranes (powered) 25 

Cab-operated or remotely operated bridge cranes 25 

(powered) 

Pendant-operated bridge cranes (powered) 10 

Bridge cranes or monorail cranes with 

hand-geared bridge, trolley, and hoist 

4.10.3 Lateral Force. The lateral force on crane runway 
beams with electrically powered trolleys shall be calcu- 
lated as 20% of the sum of the rated capacity of the 
crane and the weight of the hoist and trolley. The lateral 
force shall be assumed to act horizontally at the traction 
surface of a runway beam, in either direction perpendicu- 
lar to the beam, and shall be distributed with due regard 



Minimum Design Loads for Buildings and Other Structures 



11 



to the lateral stiffness of the runway beam and support- 
ing structure. 

4.10.4 Longitudinal Force, The longitudinal force on 
crane runway beams, except for bridge cranes with 
hand-geared bridges, shall be calculated as 10% of the 
maximum wheel loads of the crane. The longitudinal 
force shall be assumed to act horizontally at the traction 
surface of a runway beam in either direction parallel to 
the beam. 



SECTION 4.11 
REFERENCES 

Ref, 4-1 ANSI. (1988). "American National Standard Prac- 
tice for the Inspection of Elevators, Escalators, 
and Moving Walks (Inspectors' Manual)." ANSI 
A17.2. 

Ref. 4-2 ANSI/ASME. (1993). "American National Stan- 
dard Safety Code for Elevators and Escalators." 
ANSI/ASME A1ZL 



TABLE 4-1 
MINIMUM UNIFORMLY DISTRIBUTED LIVE LOADS, t > AND MINIMUM CONCENTRATED LIVE LOADS 



Occupancy or Use 


Uniform psf 

(kN/m 2 ) 


Cone, lbs 
(kN) 


Apartments (see residential) 






Access floor systems 
Office use 
Computer use 


50 (2.4) 
100 (4.79) 


2000 (8.9) 
2000 (8.9) 


Armories and drill rooms 


150(7.18) 




Assembly areas and theaters 
Fixed seats (fastened to floor) 
Lobbies 
Movable seats 
Platforms (assembly) 
Stage floors 


60 (2.87) 
100 (4.79) 
100 (4.79) 
100(4.79) 
150 (7.18) 




Balconies (exterior) 

On one- and two-family residences only, and not exceeding 100 ft. 2 (9.3 m 2 ) 


100 (4.79) 
60 (2.87) 




Bowling alleys, poolrooms, and similar recreational areas 


75 (3.59) 




Catwalks for maintenance access 


40 (1.92) 


300 (1.33) 


Corridors 
First floor 
Other floors, same as occupancy served except as indicated 


100 (4.79) 




Dance halls and ballrooms 


100 (4.79) 




Decks (patio and roof) 

Same as area served, or for the type of occupancy accommodated 






Dining rooms and restaurants 


100 (4.79) 




Dwellings (see residential) 






Elevator machine room grating (on area of 4 in. 2 (2580 mm 2 )) 




300(1.33) 


Finish light floor plate construction (on area of 1 in. 2 (645 mm 2 )) 




200 (0.89) 


Fire escapes 

On single-family dwellings only 


100 (4,79) 
40 (1.92) 




Fixed ladders 




See 
Section 4.4 


Garages (passenger vehicles only) 
Trucks and buses 


40(1.92) 

Not* 


Note (1) 

5(2) 



(continued) 



12 



ASCE 7-02 



TABLE 4-1 — continued 
MINIMUM UNIFORMLY DISTRSBUTED LIVE LOADS, L , AND MINIMUM CONCENTRATED LIVE LOADS 



Occupancy or Use 


Uniform psf 
(kU/m 2 ) 


Cone, lbs 
(kN) 


Grandstands (see stadium and arena bleachers) 






Gymnasiums, main floors, and balconies 


100 (4.79) Note (4) 




Handrails, guardrails, and grab bars 


See Section 4.4 


Hospitals 

Operating rooms, laboratories 

Private rooms 

Wards 

Corridors above first floor 


60 (2.87) 
40(1.92) 
40(1.92) 
80 (3.83) 


1000 (4.45) 
1000 (4.45) 
1000 (4.45) 
1000 (4.45) 


Hotels (see residential) 






Libraries 

Reading rooms 

Stack rooms 

Corridors above first floor 


60 (2.87) 

150 (7.18) Note (3) 

80 (3.83) 


1000 (4.45) 
1000 (4.45) 
1000 (4.45) 


Manufacturing 
Light 
Heavy 


125 (6.00) 
250(11.97) 


2000 (8.90) 
3000 (13.40) 


Marquees and canopies 


75 (3.59) 




Office buildings 
File and computer rooms shall be designed for heavier 

loads based on anticipated occupancy 
Lobbies and first floor corridors 
Offices 
Corridors above first floor 


100 (4.79) 
50 (2.40) 
80 (3.83) 


2000 (8.90) 
2000 (8.90) 
2000 (8.90) 


Penal institutions 
Cell blocks 
Corridors 


40 (1.92) 
100 (4.79) 




Residential 

Dwellings (one- and two-family) 
Uninhabitable attics without storage 
Uninhabitable attics with storage 
Habitable attics and sleeping areas 
All. other areas except stairs and balconies 

Hotels and miiltifamily houses 

Private rooms and corridors serving them 
Public rooms and corridors serving them 


10 (0.48) 
20 (0.96) 
30(1.44) 
40 (1.92) 

40 (1.92) 
100 (4.79) 




Reviewing stands, grandstands, and bleachers 


100 (4.79) Note (4) 




Roofs 


See Sections 4.3 and 4.9 



(continued) 



Minimum Design Loads for Buildings and Other Structures 



13 



TABLE 4-1 — continued 
MINIMUM UNIFORMLY DISTRIBUTED LIVE LOADS, L , AND MINIMUM CONCENTRATED LIVE 

LOADS 



Occupancy or Use 


Uniform psf 
(kN/m 2 ) 


Cone, lbs 
(kN) 


Schools 
Classrooms 

Corridors above first floor 
First floor corridors 


40 (1.92) 
80 (3.83) 
100 (4.79) 


1000 (4.45) 
1000 (4.45) 
1000 (4.45) 


Scuttles, skylight ribs, and accessible ceilings 




200 (9.58) 


Sidewalks, vehicular driveways, and yards subject to 
trucking 


250(11.97) 

Note (5) 


8000 (35.60) 
Note (6) 


Stadiums and arenas 
Bleachers 
Fixed Seats (fastened to floor) 


100 (4.79) Note (4) 
60 (2.87) Note (4) 




Stairs and exit-ways 

One- and two-family residences only 


100 (4.79) 
40 (1.92) 


Note (7) 


Storage areas above ceilings 


20 (0.96) 




Storage warehouses (shall be designed for heavier loads 
if required for anticipated storage) 

Light 

Heavy 


125 (6,00) 
250(11.97) 




Stores 
Retail 

First floor 
Upper floors 
Wholesale, all floors 


100 (4.79) 
75 (3.59) 
125 (6.00) 


1000 (4.45) 
1000 (4.45) 
1000 (4.45) 


Vehicle barriers 


See Section 4.4 


Walkways and elevated platforms (other than exit-ways) 


60 (2.87) 




Yards and terraces, pedestrians 


100 (4.79) 





Notes 

(1 ) Floors in garages or portions of building used for the storage of motor vehicles shall be designed for the uniformly distributed 
live loads of Table 4-1 or the following concentrated load: (1) for garages restricted to passenger vehicles accommodating 
not more than nine passengers, 3000 lb (13.35 kN) acting on an area of 4.5 in. by 4.5 in. (1 14 mm by 1 14 mm, footprint of 
a jack); (2) for mechanical parking structures without slab or deck which are used for storing passenger car only, 2250 lb 
(10 kN) per wheel. 

(2) Garages accommodating trucks and buses shall be designed in accordance with an approved method, which contains 
provisions for truck and bus loadings. 

(3) The loading applies to stack room floors that support nonmobile, double-faced library bookstacks subject to the following 
limitations; 

a. The nominal bookstack unit height shall not exceed 90 in. (2290 mm); 

b. The nominal shelf depth shall not exceed 12 in. (305 mm) for each face; and 

c. Parallel rows of double-faced bookstacks shall be separated by aisles not less than 36 in. (914 mm) wide. 

(4) In addition to the vertical live loads, the design shall include horizontal swaying forces applied to each row of the seats as 
follows: 24 lbs/ linear ft of seat applied in a direction parallel to each row of seats and 10 lbs/ linear ft of seat applied in a 
direction perpendicular to each row of seats. The parallel and perpendicular horizontal swaying forces need not be applied 
simultaneously. 

(5) Other uniform loads in accordance with an approved method, which contains provisions for truck loadings, shall also be 
considered where appropriate. 

(6) The concentrated wheel load shall be applied on an area of 4.5 in. by 4.5 in. (114 mm by 114 mm, footprint of a jack). 

(7) Minimum concentrated load on stair treads (on area of 4 in. 2 (2580 mm 2 )) is 300 lbs (1.33 kN). 



14 



ASCE 7-02 



TABLE 4-2 
LIVE LOAD ELEMENT FACTOR, K LL 



Element 


K LL (Note 1) 


Interior Columns 

Exterior Columns without cantilever slabs 


4 

4 


Edge Columns with cantilever slabs 


3 


Corner Columns with cantilever slabs 
Edge Beams without cantilever slabs 
Interior Beams 


2 
2 
2 


All Other Members Not Identified Above 
including: 

Edge Beams with cantilever slabs 
Cantilever Beams 
One-way Slabs 
Two-way Slabs 

Members without provisions for 
continuous shear transfer normal 
to their span 


1 



Note 1. In lieu of the values above, Kn is permitted to be calculated. 



Minimum Design Loads for Buildings and Other Structures 



15 



SECTION 5-0 

SOIL AND HYDROSTATIC PRESSURE AND FLOOD LOADS 



SECTION 5.1 
PRESSURE ON BASEMENT WALLS 

In the design of basement walls and similar approximately 
vertical structures below grade, provision shall be made 
for the lateral pressure of adjacent soil. Due allowance 
shall be made for possible surcharge from fixed or moving 
loads. When a portion or the whole of the adjacent soil is 
below a free-water surface, computations shall be based on 
the weight of the soil diminished by buoyancy, plus full 
hydrostatic pressure. 

Basement walls shall be designed to resist lateral soil 
loads. Soil loads specified in Table 5-1 shall be used as 
the minimum design lateral soil loads unless specified 
otherwise in a soil investigation report approved by the 
authority having jurisdiction. The lateral pressure from 
surcharge loads shall be added to the lateral earth pressure 
load. The lateral pressure shall be increased if soils with 
expansion potential are present at the site as determined by 
a geotechnical investigation. 



SECTION 5.2 
UPLIFT ON FLOORS AND FOUNDATIONS 

In the design of basement floors and similar approximately 
horizontal elements below grade, the upward pressure 
of water, where applicable, shall be taken as the full 
hydrostatic pressure applied over the entire area. The 
hydrostatic head shall be measured from the underside of 
the construction. Any other upward loads shall be included 
in the design. 

Where expansive soils are present under foundations or 
slabs-on-ground, the foundations, slabs, and other compo- 
nents shall be designed to tolerate the movement or resist 
the upward pressures caused by the expansive soils, or the 
expansive soil shall be removed or stabilized around and 
beneath the structure. 



SECTION 5.3 
FLOOD LOADS 

The provisions of this section apply to buildings and other 
structures located in areas prone to flooding as defined on 
a flood hazard map. 

5.3.1 Definitions. The following definitions apply to the 
provisions of Section 5.3. 



APPROVED. Acceptable to the authority having 
jurisdiction. 

BASE FLOOD. The flood having a 1% chance of being 
equaled or exceeded in any given year. 

BASE FLOOD ELEVATION (BFE). The elevation of 
flooding, including wave height, having a 1% chance of 
being equaled or exceeded in any given year. 

BREAKAWAY WALL. Any type of wall subject to flood- 
ing that is not required to provide structural support to a 
building or other structure, and that is designed and con- 
structed such that, under base flood or lesser flood condi- 
tions, it will collapse in such a way that: (1) it allows the 
free passage of floodwaters, and (2) it does not damage the 
structure or supporting foundation system. 

COASTAL A-ZONE. An area within a Special Flood 
Hazard Area, landward of a V-Zone or landward of an 
open coast without mapped V-Zones. To be classified as a 
Coastal A-Zone, the principal source of flooding must be 
astronomical tides, storm surges, seiches, or tsunamis, not 
riverine flooding. 

COASTAL HIGH-HAZARD AREA (V-ZONE). An area 
within a Special Flood Hazard Area, extending from off- 
shore to the inland limit of a primary frontal dune along 
an open coast, and any other area that is subject to high- 
velocity wave action from storms or seismic sources. This 
area is designated on FIRMs as V, VE, VO, or VI -30. 

DESIGN FLOOD. The greater of the following two flood 
events: (1) the Base Flood, affecting those areas identified 
as Special Flood Hazard Areas on the community's FIRM; 
or (2) the flood corresponding to the area designated as a 
Flood Hazard Area on a community's Flood Hazard Map 
or otherwise legally designated. 

DESIGN FLOOD ELEVATION (DFE). The elevation of 
the Design Flood, including wave height, relative to the 
datum specified on a community's Flood Hazard Map. 

FLOOD HAZARD AREA. The area subject to flooding 
during the Design Flood. 

FLOOD HAZARD MAP. The map delineating Flood 
Hazard Areas adopted by the authority having jurisdiction. 

FLOOD INSURANCE RATE MAP (FIRM). An official 
map of a community on which the Federal Insurance 
and Mitigation Administration has delineated both Special 



Minimum Design Loads for Buildings and Other Structures 



17 



Flood Hazard Areas and the risk premium zones applicable 
to the community. 

SPECIAL FLOOD HAZARD AREA (AREA OF SPE- 
CIAL FLOOD HAZARD). The land in the floodplain 
subject to a 1% or greater chance of flooding in any given 
year. These areas are delineated on a community's Flood 
Insurance Rate Map (FIRM) as A-Zones (A, AE, A 1-30, 
A99, AR, AO, or AH) or V-Zones (V, VE, VO, or Vl-30). 

53.2 Design Requirements. 

5.3.2.1 Design Loads. Structural systems of buildings 
or other structures shall be designed, constructed, con- 
nected, and anchored to resist flotation, collapse, and 
permanent lateral displacement due to action of flood 
loads associated with the design flood (see Section 5.3.3) 
and other loads in accordance with the load combinations 
of Section 2. 

53.2.2 Erosion and Scour. The effects of erosion and 
scour shall be included in the calculation of loads on 
buildings and other structures in flood hazard areas. 

53.2.3 Loads on Breakaway Walls. Walls and parti- 
tions required by Ref. 5-1, to break away, including their 
connections to the structure, shall be designed for the 
largest of the following loads acting perpendicular to 
the plane of the wall: 

1. The wind load specified in Section 6. 

2. The earthquake load specified in Section 9. 

3. 10 psf (0.48 kN/m 2 ). 

The loading at which breakaway walls are intended to 
collapse shall not exceed 20 psf (0.96 kN/m 2 ) unless the 
design meets the following conditions: 

1. Breakaway wall collapse is designed to result from 
a flood load less than that which occurs during the 
base flood; and 

2. The supporting foundation and the elevated portion 
of the building shall be designed against collapse, 
permanent lateral displacement, and other structural 
damage due to the effects of flood loads in combi- 
nation with other loads as specified in Section 2. 

533 Loads During Flooding. 

5.33.1 Load Basis. In flood hazard areas, the structural 
design shall be based on the design flood. 

533.2 Hydrostatic Loads. Hydrostatic loads caused 
by a depth of water to the level of the design flood 
elevation shall be applied over all surfaces involved, both 
above and below ground level, except that for surfaces 



exposed to free water, the design depth shall be increased 
by 1 ft (0.30 m). 

Reduced uplift and lateral loads on surfaces of 
enclosed spaces below the design flood elevation shall 
apply only if provision is made for entry and exit 
of floodwater. 

5.333 Hydrodynarak Loads. Dynamic effects of 
moving water shall be determined by a detailed analysis 
utilizing basic concepts of fluid mechanics. 

Exception: Where water velocities do not exceed 
10 ft/sec (3.05 m/s), dynamic effects of moving water 
shall be permitted to be converted into equivalent 
hydrostatic loads by increasing the design flood ele- 
vation for design purposes by an equivalent surcharge 
depth, d }u on the headwater side and above the ground 
level only, equal to: 



aV 2 
~2g 



(Eq. 5=1) 



where 



V = average velocity of water in ft/sec (m/s) 
g = acceleration due to gravity, 

32.2 ft/sec (9.81 m/s 2 ) 
a = coefficient of drag or shape factor (not less 

than 1.25) 

The equivalent surcharge depth shall be added to 
the design flood elevation design depth and the resul- 
tant hydrostatic pressures applied to, and uniformly 
distributed across, the vertical projected area of the 
building or structure which is perpendicular to the 
flow. Surfaces parallel to the flow or surfaces wet- 
ted by the tailwater shall be subject to the hydro- 
static pressures for depths to the design flood eleva- 
tion only. 

533.4 Wave Loads. Wave loads shall be determined 
by one of the following three methods: (1) using the ana- 
lytical procedures outlined in this section, (2) by more 
advanced numerical modeling procedures or, (3) by lab- 
oratory test procedures (physical modeling). 

Wave loads are those loads that result from water 
waves propagating over the water surface and striking a 
building or other structure. Design and construction of 
buildings and other structures subject to wave loads shall 
account for the following loads: waves breaking on any 
portion of the building or structure; uplift forces caused 
by shoaling waves beneath a building or structure, or 
portion thereof; wave runup striking any portion of the 
building or structure; wave-induced drag and inertia 
forces; wave-induced scour at the base of a building 
or structure, or its foundation. Wave loads shall be 
included for both V-Zones and A-Zones. In V-Zones, 



18 



ASCE 7-02 



waves are 3 ft (0.91 m) high, or higher; in coastal 
floodplains landward of the V-Zone, waves are less than 
3 ft high (0.91 m). 

Nonbreaking and broken wave loads shall be calcu- 
lated using the procedures described in Sections 5.3.3.2 
and 5.3.3.3 to calculate hydrostatic and hydrody- 
namic loads. 

Breaking waves loads shall be calculated using 
the procedures described in Sections 5.3.3.4.1 through 
5.3.3.4.4. Breaking wave heights used in the procedures 
described in Sections 5.3.3.4.1 through 5.3.3.4.4 shall 
be calculated for V Zones and Coastal A Zones using 
Eqs. 5-2 and 5-3. 



H b = 0.78 d s 



(Eq. 5-2) 



where 



Hb = breaking wave height in ft (m) 
d s — local Stillwater depth in ft (m) 

The local Stillwater depth shall be calculated using 
Eq. 5-3, unless more advanced procedures or laboratory 
tests permitted by this section are used. 



d s = 0.65(BFE-G) 



(Eq. 5-3) 



where 



BFE = Base Flood Elevation in ft (m) 
G = Ground elevation in ft (m) 

5.3.3.4.1 Breaking Wave Loads on Vertical Pilings 
and Columns. The net force resulting from a break- 
ing wave acting on a rigid vertical pile or column 
shall be assumed to act at the Stillwater elevation and 
shall be calculated by the following: 



F D = 0.5y w C D DH£ 



(Eq. 5-4) 



where 



Fd = net wave force, in pounds (kN) 

y w = unit weight of water, in pounds per cubic ft 

(kN/m 3 ), = 62.4 pcf (9.80 kN/m 3 ) for fresh 

water and 64.0 pcf (10.05 kN/m 3 ) for 

salt water 
C D = coefficient of drag for breaking waves, = 1.75 

for round piles or columns, and — 2.25 for 

square piles or columns 
D = pile or column diameter, in ft (m) for circular 

sections, or for a square pile or column, 1.4 

times the width of the pile or column in 

ft (m). 
Hfj = breaking wave height, in ft (m) 

53.3.4.2 Breaking Wave Loads on Vertical Walls. 
Maximum pressures and net forces resulting from 



a normally incident breaking wave (depth- limited in 
size, with H h = 0.78i v ) acting on a rigid vertical wall 
shall be calculated by the following: 



*m ax — ^pYvj^s i *--^Ywd$ 



and 



F t = l.lC p Ywdf + 2Ay w d; 



(Eq. 5-5) 



(Eq. 5-6) 



where 



p max = maximum combined dynamic (C p y w d s ) and 
static (1.2y w d s )wave pressures, also referred 
to as shock pressures in lbs/ft 2 (kN/m 2 ) 

F t = net breaking wave force per unit length of 
structure, also referred to as shock, impulse 
or wave impact force in lbs/ft (kN/m), 
acting near the Stillwater elevation 

C p = dynamic pressure coefficient 

(1.6 < C p < 3.5) (see Table 5-2) 

y w = unit weight of water, in lbs/ft 3 (kN/m 3 ), 

= 62.4 pcf (9.80 kN/m 3 ) for fresh water and 
64.0 pcf (10.05 kN/m 3 ) for salt water 

d s — Stillwater depth in ft (m) at base of building 
or other structure where the wave breaks 

This procedure assumes the vertical wall causes a 
reflected or standing wave against the waterward side 
of the wall with the crest of the wave at a height of 
1.2 d s above the Stillwater level. Thus, the dynamic 
static and total pressure distributions against the wall 
are as shown in Figure 5-1. 

This procedure also assumes the space behind 
the vertical wall is dry, with no fluid balancing the 
static component of the wave force on the outside 
of the wall. If free water tx\y--3 behind the wall, a 
portion of the hydrostatic component of the wave 
pressure and force disappears (see Figure 5-2) and 
the net force shall be computed by Eq. 5-7 (the 
maximum combined wave pressure is still computed 
with Eq. 5-5). 



F, = l.l C p y w d 2 s +\.9y w d 2 s 



(Eq. 5-7) 



where 



F t — net breaking wave force per unit length of 

structure, also referred to as shock, impulse, or 
wave impact force in lbs/ft (kN/m), acting 
near the Stillwater elevation 

C p = dynamic pressure coefficient (1.6 < C p < 3.5) 
(see Table 5-2) 

y w = unit weight of water, in lbs/ft 3 (kN/m 3 ), 

= 62.4 pcf (9.80 kN/m 3 ) for fresh water and 
64.0 pcf (10.05 kN/m 3 ) for salt water 

d s = Stillwater depth in ft (m) at base of building or 
other structure where the wave breaks 



Minimum Design Loads for Buildings and Other Structures 



19 



53.3.4.3 Breaking Wave Loads on Nonvertical 
Walls. Breaking wave forces given by Eq. 5-6 and 
Eq. 5-7 shall be modified in instances where the walls 
or surfaces upon which the breaking waves act are 
nonvertical. The horizontal component of breaking 
wave force shall be given by: 



F nv = Ft sin 2 a 



(Eq. 5-8) 



where 

r nv — 



horizontal component of breaking wave force 

in lbs/ft (kN/m) 
F t = net breaking wave force acting on a vertical 

surface in lbs/ft (kN/m) 
a = vertical angle between nonvertical surface 

and the horizontal 

5.3.3.4.4 Breaking Wave Loads from Obliquely 
Incident Waves. Breaking wave forces given by 
Eq. 5-6 and Eq, 5-7 shall be modified in instances 
where waves are obliquely incident. Breaking wave 
forces from non-normally incident waves shall be 
given by: 

F oi = F,sin 2 <* (Eq. 5-9) 



where 

F i = horizontal component of obliquely incident 

breaking wave force in lbs/ft (kN/m) 
F t — net breaking wave force (normally incident 
waves) acting on a vertical surface in 
lbs/ft (kN/m) 
a = horizontal angle between the direction of 
wave approach and the vertical surface 

5.3.3.5 Impact Loads. Impact loads are those that 
result from debris, ice, and any object transported by 
floodwaters striking against buildings and structures, 
or parts thereof. Impact loads shall be determined 
using a rational approach as concentrated loads acting 
horizontally at the most critical location at or below the 
design flood elevation. 



SECTION 5.4 
REFERENCE 

Ref. 5-1 ASCE. (1998). "Flood Resistant Design and Con- 
struction." SEI/ASCE 24-98. 



Vertical Wall 



1.2 cU 



y 



d @ 




Crest of reflected wave 



Dynamic pressure 



iii 

i i i t v * ■ 
•I'M* !»,» »;»:» 

I (It til !*•*»*! 

1 I I t ( I I » * t 
» II I I til I » 

hViVi Vt'tV»Vi' 
' ■ i i i » • • ■ * * ' 

fc'i't'i'i 1 ' 



Crest of incident wave 



0,55 d s 



SWL (Stillwater level) 



Hydrostatic pressure 



I'lVl'lVl VlVl't'tVl 



Ground elevation 



FIGURE 5.1 
NORMALLY INCIDENT BREAKING WAVE PRESSURES AGAINST A VERTICAL WALL (SPACE BEHIND VERTICAL WALL SS DRY) 



20 



ASCE 7-02 



Vertical Wall 



Crest of reflected wave 



dynamic pressure 



crest of incident wave 




SWL (Stillwater level) 



FIGURE 5.2 
NORMALLY INCIDENT BREAKING WAVE PRESSURES AGAINST A VERTICAL WALL (STILLWATER LEVEL EQUAL 

ON BOTH SIDES OF WALL) 



Minimum Design Loads for Buildings and Other Structures 



21 



TABLE 5-1 
DESIGN LATERAL SOIL LOAD 



Description of Backfsil Material 


Unified Soil 
Classification 


Design Lateral Soil 

Load (Note A) psf/ft of depth 

(kN/m 2 /m of depth) 


Well-graded, clean gravels; gravel-sand mixes 


GW 


35 (5.50) Note C 


Poorly graded clean gravels; gravel -sand mixes 


GP 


35 (5.50) Note C 


Silty gravels, poorly graded gravel-sand mixes 


GM 


35 (5.50) Note C 


Clayey gravels, poorly graded gravel-and-clay mixes 


GC 


45 (7.07) Note C 


Well-graded, clean sands; gravelly-sand mixes 


sw 


35 (5.50) Note C 


Poorly graded clean sands; sand-gravel mixes 


SP 


35 (5.50) Note C 


Silty sands, poorly graded sand-silt mixes 


SM 


45 (7.07) Note C 


Sand-silt clay mix with plastic fines 


SM-SC 


85 (13.35) Note D 


Clayey sands, poorly graded sand-clay mixes 


sc 


85 (13.35) Note D 


Inorganic silts and clayey silts 


ML 


85 (13.35) Note D 


Mixture of inorganic silt and clay 


ML-CL 


85 (13.35) Note D 


Inorganic clays of low to medium plasticity 


CL 


100 (15.71) 


Organic silts and silt-clays, low plasticity 


OL 


NoteB 


Inorganic clayey silts, elastic silts 


MH 


NoteB 


Inorganic clays of high plasticity 


CH 


Note B 


Organic clays and silty clays 


OH 


Note B 



Note A. Design lateral soil loads are given for moist conditions for the specified soils at their optimum densities. Actual held conditions 

shall govern. Submerged or saturated soil pressures shall include the weight of the buoyant soil plus the hydrostatic loads. 

Note B. Unsuitable as backfill material. 

Note C. For relatively rigid walls, as when braced by floors, the design lateral soil load shall be increased for sand and gravel type soils 

to 60 psf (9.43 kN/m 2 ) per ft (meter) of depth. Basement walls extending not more than 8 ft (2.44 m) below grade and supporting light 

floor systems are not considered as being relatively rigid walls. 

Note D. For relatively rigid walls, as when braced by floors, the design lateral load shall be increased for silt and clay type oils to 

100 psf (15.71 kN/m 2 ) per ft (meter) of depth. Basement walls extending not more than 8 ft (2.44 m) below grade and supporting light 

floor systems are not considered as being relatively rigid walls. 

TABLE 5-2 
VALUE OF DYNAMBC PRESSURE 

COEFFICIENT, C p 



Building Category 


Op 


I 


1.6 


II 


2.8 


III 


3.2 


IV 


3.5 



22 



ASCE 7-02 



SECTION 6.0 

WIND LOADS 



SECTION 6.1 
GENERAL 

6.1.1 Scope. Buildings and other structures, including the 
main wind force-resisting system and all components and 
cladding thereof, shall be designed and constructed to resist 
wind loads as specified herein. 



6.1.2 Allowed Procedures. The design wind loads for 
buildings and other structures, including the main wind 
force-resisting system and component and cladding ele- 
ments thereof, shall be determined using one of the 
following procedures: (1) Method 1 — Simplified Proce- 
dure as specified in Section 6.4 for buildings meeting the 
requirements specified therein; (2) Method 2 — Analytical 
Procedure as specified in Section 6.5 for buildings meeting 
the requirements specified therein; (3) Method 3 — Wind 
Tunnel Procedure as specified in Section 6.6. 



6.13 Wind Pressures Acting on Opposite Faces of 
Each Building Surface. In the calculation of design wind 
loads for the main wind force-resisting system and for 
components and cladding for buildings, the algebraic sum 
of the pressures acting on opposite faces of each building 
surface shall be taken into account. 



6.1.4 Minimum Design Wind Loading. The design wind 
load, determined by any one of the procedures speci- 
fied in Section 6.1.2, shall be not less than specified in 
this Section. 



6.1.4.1 Main Wind Force-Resisting System. The wind 
load to be used in the design of the main wind force- 
resisting system for an enclosed or partially enclosed 
building or other structure shall not be less than 10 lb/ft 2 
(0.48 kN/m 2 ) multiplied by the area of the build- 
ing or structure projected onto a vertical plane nor- 
mal to the assumed wind direction. The design wind 
force for open buildings and other structures shall be 
not less than 10 lb/ft 2 (0.48 kN/m 2 ) multiplied by the 
area Af. 



6.1.4.2 Components and Cladding. The design wind 
pressure for components and cladding of buildings shall 
not be less than a net pressure of 10 lb/ft 2 (0.48 kN/m 2 ) 
acting in either direction normal to the surface. 



SECTION 6.2 
DEFINITIONS 

The following definitions apply only to the provisions of 
Section 6: 

APPROVED. Acceptable to the authority having juris- 
diction. 

BASIC WIND SPEED, V. 3-second gust speed at 33 ft 
(10 m) above the ground in Exposure C (see Section 6.5.6.3) 
as determined in accordance with Section 6.5.4. 

BUILDING, ENCLOSED. A building that does not 
comply with the requirements for open or partially 
enclosed buildings. 

BUILDING ENVELOPE. Cladding, roofing, exterior 
walls, glazing, door assemblies, window assemblies, 
skylight assemblies, and other components enclosing 
the building. 

BUILDING AND OTHER STRUCTURE, FLEXIBLE. 
Slender buildings and other structures that have a funda- 
mental natural frequency less than 1 Hz. 

BUILDING, LOW-RISE. Enclosed or partially enclosed 
buildings that comply with the following conditions: 

1. mean roof height h less than or equal to 60 ft 
(18 ra); and 

2. mean roof height h does not exceed least horizon- 
tal dimension. 

BUILDING, OPEN. A building having each wall at least 
80% open. This condition is expressed for each wall by the 
equation A > 0.8A# where 

A = total area of openings in a wall that receives positive 

external pressure, in ft 2 (m 2 ) 
A g = the gross area of that wall in which A is identified, 

in ft 2 (m 2 ) 

BUILDING, PARTIALLY ENCLOSED. A building that 
complies with both of the following conditions: 

1. the total area of openings in a wall that receives 
positive external pressure exceeds the sum of the 
areas of openings in the balance of the building 
envelope (walls and roof) by more than 10%, and 

2. the total area of openings in a wall that receives 
positive external pressure exceeds 4 ft 2 (0.37 m 2 ) or 



Minimum Design Loads for Buildings and Other Structures 



23 



1% of the area of that wall, whichever is smaller, 
and the percentage of openings in the balance of the 
building envelope does not exceed 20%. 

These conditions are expressed by the following equations: 



1. A > l.lQAoi 

2. A > Aft 2 (0.37 m 2 ) or 



> 0.01 A g , 



whichever is 



smaller, and A i/A„i < 0.20 where 



A , A g are as defined for Open Building 

A oi — the sum of the areas of openings in the 

building envelope (walls and roof) not 

including A , in ft 2 (m 2 ) 
A g i = the sum of the gross surface areas of the 

building envelope (walls and roof) not 

including A g , in ft 2 (m 2 ) 

BUILDING OR OTHER STRUCTURE, REGULAR 
SHAPED. A building or other structure having no unusual 
geometrical irregularity in spatial form. 

BUILDING OR OTHER STRUCTURES, RIGID. A 
building or other structure whose fundamental frequency 
is greater than or equal to 1 Hz. 

BUILDING, SIMPLE DIAPHRAGM, An enclosed or 
partially enclosed building in which wind loads are trans- 
mitted through floor and roof diaphragms to the vertical 
main wind force-resisting system. 

COMPONENTS AND CLADDING. Elements of the 
building envelope that do not qualify as part of the main 
wind force-resisting system. 

DESIGN FORCE, F. Equivalent static force to be used 
in the determination of wind loads for open buildings and 
other structures. 

DESIGN PRESSURE, p. Equivalent static pressure to be 
used in the determination of wind loads for buildings. 

EFFECTIVE WIND AREA. The area used to determine 
GC P . For component and cladding elements, the effective 
wind area in Figures 6-11 through 6-17 is the span length 
multiplied by an effective width that need not be less 
than one-third the span length. For cladding fasteners, the 
effective wind area shall not be greater than the area that 
is tributary to an individual fastener. 

ESCARPMENT. Also known as scarp, with respect to 
topographic effects in Section 6.5.7, a cliff or steep slope 
generally separating two levels or gently sloping areas (see 
Figure 6-4). 

GLAZING. Glass or transparent or translucent plastic 
sheet used in windows, doors, skylights, or curtain walls. 



GLAZING, IMPACT RESISTANT. Glazing that has 
been shown by testing in accordance with ASTM E 1886 [6- 
1] and ASTM E 1996 [6-2] or other approved test methods 
to withstand the impact of wind-borne missiles likely to be 
generated in wind-borne debris regions during design winds. 

HILL. With respect to topographic effects in Section 6.5.7, 
a land surface characterized by strong relief in any horizon- 
tal direction (see Figure 6-4). 

.HURRICANE-PRONE REGIONS. Areas vulnerable to 
hurricanes; in the United States and its territories defined as: 

1. the U.S. Atlantic Ocean and Gulf of Mexico coasts 
where the basic wind speed is greater than 90 mph, and 

2, Hawaii, Puerto Rico, Guam, Virgin Islands, and 
American Samoa. 

IMPACT-RESISTANT COVERING. A covering desig- 
ned to protect glazing, which has been shown by testing in 
accordance with ASTM E 1886 [6-1] and ASTM 1996 [6-2] 
or other approved test methods to withstand the impact of 
wind-borne debris missiles likely to be generated in wind- 
borne debris regions during design winds. 

IMPORTANCE FACTOR, I. A factor that accounts for 
the degree of hazard to human life and damage to property. 

MAIN WIND FORCE-RESISTING SYSTEM. An 
assemblage of structural elements assigned to provide sup- 
port and stability for the overall structure. The system gen- 
erally receives wind loading from more than one surface. 

MEAN ROOF HEIGHT, h. The average of the roof eave 
height and the height to the highest point on the roof sur- 
face, except that, for roof angles of less than or equal to 10 
degrees, the mean roof height shall be the roof eave height. 

OPENINGS. Apertures or holes in the building envelope 
that allow air to flow through the building envelope and 
that are designed as "open" during design winds as defined 
by these provisions. 

RECOGNIZED LITERATURE, Published research find- 
ings and technical papers that are approved. 

RIDGE. With respect to topographic effects in 
Section 6.5.7, an elongated crest of a hill characterized by 
strong relief in two directions (see Figure 6-4). 

WIND-BORNE DEBRIS REGIONS. Areas within hur- 
ricane-prone regions located 

1. within 1 mile of the coastal mean high water line 
where the basic wind speed is equal to or greater 
than 1 10 mph and in Hawaii, or 

2. in areas where the basic wind speed is equal to or 
greater than 120 mph. 



24 



ASCE 7-02 



The following 
provisions of 

A - 






A„ = 



j\ n i — 



a 
B 



b = 

Cf = 

C p ^ 

c = 

D = 

D' = 

G = 
Gf = 

GC n = 



GC P f = 



GCpi = 



SECTION 6.3 
SYMBOLS AND NOTATIONS 

I symbols and notations apply only to the 
Section 6: 

: effective wind area, in ft 2 (m 2 ); 

: area of open buildings and other structures 

either normal to the wind direction or 

projected on a plane normal to the wind 

direction, in ft 2 (m 2 ); 
= the gross area of that wall in which A is 

identified, in ft 2 (m 2 ); 
= the sum of the gross surface areas of the 

building envelope (walls and roof) not 

including A g , in ft 2 (m 2 ); 

total area of openings in a wall that receives 

positive external pressure, in ft 2 (m 2 ); 

the sum of the areas of openings in the 

building envelope (walls and roof) not 

including A , in ft 2 (m 2 ); 

total area of openings in the building 

envelope ft 2 (m 2 ); 

width of pressure coefficient zone, in ft (m); 

horizontal dimension of building measured 

normal to wind direction, in ft (m); 

mean hourly wind speed factor in Eq. 6-14 

from Table 6-2; 

3-second gust speed factor from Table 6-2; 

force coefficient to be used in determination 

of wind loads for other structures; 

external pressure coefficient to be used in 

determination of wind loads for buildings; 

turbulence intensity factor in Eq. 6-5 from 

Table 6-2 

diameter of a circular structure or member, 

in ft (m); 

depth of protruding elements such as ribs 

and spoilers, in ft (m); 

gust effect factor; 

gust effect factor for main wind 

force-resisting systems of flexible buildings 

and other structures; 

combined net pressure coefficient for a 

parapet 

product of external pressure coefficient 

and gust effect factor to be used in 

determination of wind loads for 

buildings; 

product of the equivalent external pressure 

coefficient and gust effect factor to be used 

in determination of wind loads for main 

wind force-resisting system of low-rise 

buildings; 

product of internal pressure coefficient and 

gust effect factor to be used in 

determination of wind loads for buildings; 



gQ — peak factor for background response in 

Eqs. 6-4 and 6-8; 
g R = peak factor for resonant response in 

Eq. 6-8; 
g v = peak factor for wind response in Eqs. 6-4 

and 6-8; 
H = height of hill or escarpment in Figure 6-4, 

in ft (m); 
h = mean roof height of a building or height of 
other structure, except that eave height 
shall be used for roof angle 9 of less than 
or equal to 10 degrees, in ft (m); 
/ = importance factor; 
l_ __ intensity of turbulence from Eq. 6-5; 
K\, K2, K3 — multipliers in Figure 6-4 to obtain K zt \ 
K d = wind directionality factor in Table 6-4; 
Kh = velocity pressure exposure coefficient 

evaluated at height z = h\ 
K z = velocity pressure exposure coefficient 

evaluated at height z\ 
K zt — topographic factor; 
L = horizontal dimension of a building 

measured parallel to the wind direction, in 
ft (m); 
L h = distance upwind of crest of hill or 

escarpment in Figure 6-4 to where the 
difference in ground elevation is half the 
height of hill or escarpment, in ft (m); 
L™ = integral length scale of turbulence, in ft 
(m); 
I = integral length scale factor from Table 6-2, 
ft (m); 
M = larger dimension of sign, in ft (m); 
/V — smaller dimension of sign, in ft (m); 
N\ — reduced frequency from Eq. 6-12; 
m — building natural frequency, Hz; 
p = design pressure to be used in determination 
of wind loads for buildings, in lb/ft 2 
(N/m 2 ); 
p L = wind pressure acting on leeward face in 
Figure 6-9; 
Pnet3o — net design wind pressure for exposure B at 
h = 30 ft and / = 1.0 from Figure 6-3; 
p p = combined net pressure on a parapet from 
Eq. 6-20; 
Psio = simplified design wind pressure for 

exposure B at h = 30 ft and / = 1.0 from 
Figure 6-2; 
p w = wind pressure acting on windward face in 
Figure 6-9; 
Q ~ background response factor from Eq. 6-6; 
q = velocity pressure, in lb/ft 2 (N/m 2 ); 
q h = velocity pressure evaluated at height z — h, 
in lb/ft 2 (N/m 2 ); 



Minimum Design Loads for Buildings and Other Structures 



25 



q t = velocity pressure for internal pressure 

determination; 
q p = velocity pressure at top of parapet; 
q z = velocity pressure evaluated at height z 

above ground, in lb/ft 2 (N/m 2 ); 
R — resonant response factor from Eq. 6-10; 
R B , Rh, Rjl = values from Eq. 6-13; 

R t = reduction factor from Eq. 6-16; 
R n — value from Eq. 6-1 1 ; 
r — rise-to-span ratio for arched roofs; 
V — basic wind speed obtained from Figure 6-1, 

in mph (m/s). The basic wind speed 

corresponds to a 3 -second gust speed at 

33 ft (10 m) above ground in Exposure 

Category C; 
Vi = unpartitioned internal volume ft 3 (m 3 ); 
Vj = mean hourly wind speed at height z, ft/s 

(m/s); 
W = width of building in Figures 6-12, and 

6-14A and B and width of span in 

Figures 6-13 and 6-15, in ft (m); 
X = distance to center of pressure from 

windward edge in Figure 6-18, in ft (m); 
x = distance upwind or downwind of crest in 

Figure 6-4, in ft (m); 
z = height above ground level, in ft (m); 
z = equivalent height of structure, in ft (m); 
z g — nominal height of the atmospheric 

boundary layer used in this standard. 

Values appear in Table 6-2; 
Zm[n = exposure constant from Table 6-2; 

a = 3 -sec gust speed power law exponent from 

Table 6-2; 
a = reciprocal of a from Table 6-2; 
a = mean hourly wind speed power law 

exponent in Eq. 6-14 from Table 6-2; 
/? = damping ratio, percent critical for buildings 

or other structures; 
G — ratio of solid area to gross area for open 

sign, face of a trussed tower, or lattice 

structure; 
X = adjustment factor for building height and 

exposure from Figures 6-2 and 6-3; 
e = integral length scale power law exponent in 

Eq. 6-7 from Table 6-2; 
T) = value used in Eq. 6-13 (see 

Section 6.5.8.2); 
= angle of plane of roof from horizontal, in 

degrees; 
v — height- to- width ratio for solid sign. 

SECTION 6.4 
METHOD 1 -SIMPLIFIED PROCEDURE 

6.4.1 Scope. A building whose design wind loads are 
determined in accordance with this Section shall meet 



all the conditions of 6.4.1.1 or 6.4.1.2. If a. building 
qualifies only under 6.4.1.2 for design of its components 
and cladding, then its main wind force-resisting system 
shall be designed by Method 2 or Method 3. 

6.4.1.1 Main Wind Force-Resisting Systems. For the 
design of main wind force-resisting systems the building 
must meet all of the following conditions: 

1. the building is a simple diaphragm building as 
defined in Section 6.2, 

2. the building is a low-rise building as defined in 
Section 6.2, 

3. the building is enclosed as defined in Section 6.2 
and conforms to the wind-borne debris provisions 
of Section 6.5.9.3, 

4. the building is a regular shaped building or struc- 
ture as defined in Section 6.2, 

5. the building is not classified as a flexible building 
as defined in Section 6.2, 

6. the building does not have response characteristics 
making it subject to across-wind loading, vortex 
shedding, instability due to galloping or flutter; 
and does not have a site location for which 
channeling effects or buffeting in the wake of 
upwind obstructions warrant special consideration, 

7. the building structure has no expansion joints or 
separations, 

8. the building is not subject to the topographic 
effects of 6.5.7 (i.e., K zt = 1.0), 

9. the building has an approximately symmetrical 
cross section in each direction with either a flat 
roof, or a gable or hip roof with < 45 degrees. 

6.4.1.2 Components and Cladding. For the design of 
components and cladding the building must meet all the 
following conditions: 

1. the mean roof height h < 60 ft, 

2. the building is enclosed as defined in Section 6.2 
and conforms to the wind-borne debris provisions 
of Section 6.5.9.3, 

3. the building is a regular shaped building or struc- 
ture as defined in Section 6.2, 

4. the building does not have response character- 
istics making it subject to across-wind loading, 
vortex shedding, instability due to galloping or 
flutter; and does not have a site location for 
which channeling effects or buffeting in. the wake 
of upwind obstructions warrant special consi- 
deration, 

5. the building is not subject to the topographic 
effects of Section 6.5.7 (i.e., K zt = 1.0), 



26 



ASCE 7-02 



6. the building has either a flat roof, or a gable 
roof with < 45 degrees, or a hip roof with 
< 27 degrees. 

6.4.2 Design Procedure. 

1. The basic wind speed V shall be determined in 
accordance with Section 6.5.4. The wind shall be 
assumed to come from any horizontal direction. 

2. An importance factor I shall be determined in accor- 
dance with Section 6.5.5. 

3. An exposure category shall be determined in accor- 
dance with Section 6.5.6. 

4. A height and exposure adjustment coefficient, A, shall 
be determined from Figure 6-2. 

6.4.2.1 Main Wind Force-Resisting System. Simpli- 
fied design wind pressures, p s , for the main wind force- 
resisting systems of low-rise simple diaphragm buildings 
represent the net pressures (sum of internal and external) 
to be applied to the horizontal and vertical projections 
of building surfaces as shown in Figure 6-2. For the 
horizontal pressures (Zones A, B, C, D), p s is the 
combination of the windward and leeward net pressures. 
p s shall be determined by the following equation: 



Ps = Mps 



S30 



(Eq, 6-1) 



where 



k — adjustment factor for building height and 

exposure from Figure 6-2. 
/ = importance factor as defined in Section 6.2. 
p S30 = simplified design wind pressure for exposure 

B, at h = 30 ft, and for / = 1 .0, from 

Figure 6-2. 

6.4,2.1.1 Minimum Pressures. The load effects of 
the design wind pressures from Section 6.4.2.1 shall 
not be less than the minimum load case from 
Section 6.1.4.1 assuming the pressures, p s , for Zones 
A, B, C, and D all equal to +10 psf, while assuming 
Zones E, F, G, and H all equal to psf. 

6.4,2.2 Components and Cladding. Net design wind 
pressures, p net , for the components and cladding of 
buildings designed using Method 1 represent the net 
pressures (sum of internal and external) to be applied 
normal to each building surface as shown in Figure 6-3. 
p net shall be determined by the following equation: 



Pnet = MPn 



■ertO 



(Eq. 6-2) 



where 



k = adjustment factor for building height and 
exposure from Figure 6-3. 



/ = importance factor as defined in Section 6.2. 
Puerto = net design wind pressure for exposure B, at 
h - 30 ft, and for / = 1.0, from 

Figure 6-3. 

6A2.2.1 Minimum Pressures. The positive design 
wind pressures, p net9 from Section 6,4.2.2 shall not 
be less than +10 psf, and the negative design wind 
pressures, p nett from 6.4.2.2 shall not be less than 
-10 psf. 

6*43 Air-Permeable Cladding. Design wind loads deter- 
mined from Figure 6-3 shall be used for all air-permeable 
cladding unless approved test data or recognized litera- 
ture demonstrate lower loads for the type of air-permeable 
cladding being considered. 



SECTION 6.5 

METHOD 2 - ANALYTICAL PROCEDURE 

6.5.1 Scope,, A building or other structure whose design 
wind loads are determined in accordance with this Section 
shall meet all of the following conditions: 

1. The building or other structure is a regular shaped 
building or structure as defined in Section 6.2, and 

2. The building or other structure does not have response 
characteristics making it subject to across-wind load- 
ing, vortex shedding, instability due to galloping or 
flutter; or does not have a site location for which 
channeling effects or buffeting in the wake of upwind 
obstructions warrant special consideration. 

6.5.2 Limitations. The provisions of Section 6.5 take into 
consideration the load magnification effect caused by gusts 
in resonance with along-wind vibrations of flexible build- 
ings or other structures. Buildings or other structures 
not meeting the requirements of Section 6.5.1, or hav- 
ing unusual shapes or response characteristics, shall be 
designed using recognized literature documenting such 
wind load effects or shall use the wind tunnel procedure 
specified in Section 6.6. 

6.5.2.1 Shielding. There shall be no reductions in 
velocity pressure due to apparent shielding afforded by 
buildings and other structures or terrain features. 

6.5.2.2 Air-Permeable Cladding. Design wind loads 
determined from Section 6.5 shall be used for air- 
permeable cladding unless approved test data or recog- 
nized literature demonstrate lower loads for the type of 
air-permeable cladding being considered. 



Minimum Design Loads for Buildings and Other Structures 



27 



6.5.3 Design Procedure. 

1. The basic wind speed V and wind directionality 
factor K d shall be determined in accordance with 
Section 6.5.4. 

2. An importance factor I shall be determined in 
accordance with Section 6.5.5. 

3. An exposure category or exposure categories and 
velocity pressure exposure coefficient K z or Kh, 
as applicable, shall be determined for each wind 
direction in accordance with Section 6.5.6, 

4. A topographic factor K zt shall be determined in 
accordance with Section 6.5.7, 

5. A gust effect factor G or G/> as applicable, shall be 
determined in accordance with Section 6.5.8. 

6. An enclosure classification shall be determined in 
accordance with Section 6.5.9. 

7. Internal pressure coefficient GC p i shall be deter- 
mined in accordance with Section 6.5.11.1. 

8. External pressure coefficients C p orGC P f, or force 
coefficients C f, as applicable, shall be determined 
In accordance wi th Section 6.5.11.2 or 6.5.11.3, 
respectively. 

9. Velocity pressure q z or q/ u as applicable, shall be 
determined in accordance with Section 6.5.10. 

10. Design wind loadp or F shall be determined in accor- 
dance with Sections 6.5.12 and 6.5.13, as applicable. 

6.5.4 Basic Wind Speed. The basic wind speed, V, used 
in the determination of design wind loads on buildings and 
other structures shall be as given in Figure 6-1 except as 
provided in Sections 6.5.4.1 and 6.5.4.2. The wind shall be 
assumed to come from any horizontal direction. 



terrain exposure of the anemometer have been taken 
into account. 

In hurricane-prone regions, wind speeds derived 
from simulation techniques shall only be used in lieu 
of the basic wind speeds given in Figure 6-1 when 

(1) approved simulation or extreme- value statistical- 
analysis procedures are used (the use of regional wind 
speed data obtained from anemometers is not permit- 
ted to define the hurricane wind speed risk along the 
Gulf and Atlantic coasts, the Caribbean, or Hawaii) and 

(2) the design wind speeds resulting from the study shall 
not be less than the resulting 500- year return period wind 
speed divided by VT5. 

6,5.43 Limitation. Tornadoes have not been considered 
in developing the basic wind-speed distributions. 

6.5.4.4 Wind Directionality Factor, The wind direc- 
tionality factor, K c i, shall be determined from Table 6-4. 
This factor shall only be applied when used in conjunc- 
tion with load combinations specified in Sections 2.3 

and 2.4. 

6.5.5 Importance Factor. An importance factor, /, for 
the building or other structure shall be determined from 
Table 6-1 based on building and structure categories listed 
in Table 1-1. 

6.5.6 Exposure. For each wind direction considered, an 
exposure category that adequately reflects the characteris- 
tics of ground roughness and surface irregularities shall be 
determined for the site at which the building or structure 
Is to be constructed. Account shall be taken of varia- 
tions in ground surface roughness that arises from natural 
topography and vegetation as well as constructed features. 



6.5.4.1 Special Wind Regions, The basic wind speed 
shall be increased where records or experience indicate 
that the wind speeds are higher than those reflected 
in Figure 6-1. Mountainous terrain, gorges, and spe- 
cial regions shown in Figure 6-1 shall be examined for 
unusual wind conditions. The authority having juris- 
diction shall, if necessary, adjust the values given in 
Figure 6-1 to account for higher local wind speeds. Such 
adjustment shall be based on meteorological informa- 
tion and an estimate of the basic wind speed obtained in 
accordance with the provisions of Section 6.5.4.2. 

6.5.4.2 Estimation of Basic Wind Speeds from 
Regional Climatic Data. Regional climatic data shall 
only be used in lieu of the basic wind speeds given in 
Figure 6-1 when; (1) approved extreme- value statistical- 
analysis procedures have been employed in reducing 
the data; and (2) the length of record, sampling error, 
averaging time, anemometer height, data quality, and 



6.5.6.1 Wind Directions and Sectors. For each selected 
wind direction at which the wind loads are to be evaluated, 
the exposure of the building or structure shall be deter- 
mined for the two upwind sectors extending 45 degrees 
either side of the selected wind direction. The exposures 
in these two sectors shall be determined in accordance 
with Sections 6.5.6.2 and 6.5.6.3 and the exposure result- 
ing in the highest wind loads shall be used to represent 
the winds from that direction. 

6.5.6.2 Surface Roughness Categories. A ground sur- 
face roughness within each 45-degree sector shall be 
determined for a distance upwind of the site as defined 
in Section 6.5.6.3 from the categories defined below, for 
the purpose of assigning an. exposure category as defined 
in Section 6.5.6.3. 

Surface Roughness B: Urban and suburban areas, 
wooded areas or other terrain with numerous 



28 



ASCE 7»02 



closely spaced obstructions having the size of 

single-family dwellings or larger. 
Surface Roughness C: Open terrain with scattered 

obstructions having heights generally less than 

30 ft (9.1m). This category includes flat open 

country, grasslands, and all water surfaces in 

hurricane-prone regions. 
Surface Roughness D: Flat, unobstructed areas and 

water surfaces outside hurricane-prone regions. 

This category includes smooth mud flats, salt flats, 

and unbroken ice. 

6.5.63 Exposure Categories. 

Exposure B: Exposure B shall apply where the ground 
surface roughness condition, as defined by Surface 
Roughness B, prevails in the upwind direction for 
a distance of at least 2630 ft (800 m) or 10 times 
the height of the building, whichever is greater. 

Exception: For buildings whose mean roof 
height is less than or equal to 30 ft (9.1 m), 
the upwind distance may be reduced to 
1500 ft (457 m). 

Exposure C: Exposure C shall apply for all cases 
where exposures B or D do not apply. 

Exposure D: Exposure D shall apply where the 
ground surface roughness, as defined by surface 
roughness D, prevails in the upwind direction for a 
distance at least 5000 ft (1524 m) or 10 times the 
building height, whichever is greater. Exposure D 
shall extend inland from the shoreline for a distance 
of 660 ft (200 m) or 10 times the height of the 
building, whichever is greater. 

For a site located in the transition zone between expo- 
sure categories, the category resulting in the largest 
wind forces shall be used. Exception: An inter- 
mediate exposure between the above categories is 
permitted in a transition zone provided that it is 
determined by a rational analysis method defined 
in the recognized literature. 

6.5.6,4 Exposure Category for Main Wind 
Force-Resisting Systems* 

6*5.6 A 1 Buildings and Other Structures. For each 
wind direction considered, wind loads for the design 
of the main wind force-resisting system determined 
from Figure 6-6 shall be based on the exposure 
categories defined in Section 6.5.6.3. 

6.5*6,4.2 Low-Rise Buildings. Wind loads for the 
design of the main wind force-resisting systems 
for low-rise buildings shall be determined using a 



velocity pressure q\ x based on the exposure resulting 
in the highest wind loads for any wind direction at the 
site when external pressure coefficients GC p f given 
in Figure 6-10 are used. 

6.5.6.5 Exposure Category for Components and 
Cladding. 

6.5.6.5.1 Buildings with Mean Roof Height h Less 
Than or Equal to 60 ft (18 m). Components and 
cladding for buildings with a mean roof height h of 
60 ft (18 m) or less shall be designed using a velocity 
pressure qj t based on the exposure resulting in the 
highest wind loads for any wind direction at the site. 

6.5.6.5.2 Buildings with Mean Roof Height h 
Greater Than 60 ft (18 m) and Other Structures. 
Components and cladding for buildings with a mean 
roof height h in excess of 60 ft (18 m) and for 
other structures shall be designed using the exposure 
resulting in the highest wind loads for any wind 
direction at the site. 

6.5.6.6 Velocity Pressure Exposure Coefficient. Based 
on the exposure category determined in Section 6.5.6.3, 
a velocity pressure exposure coefficient K z or K h , as 
applicable, shall be determined from Table 6-3. 

6.5.7 Topographic Effects. 

6.5.7.1 Wind Speed-Up over Hills, Ridges, and Escarp- 
ments. Wind speed-up effects at isolated hills, ridges, 
and escarpments constituting abrupt changes in the 
general topography, located in any exposure category, 
shall be included in the design when buildings and other 
site conditions and locations of structures meet all of the 
following conditions: 

1. The hill, ridge, or escarpment is isolated and 
unobstructed upwind by other similar topographic 
features of comparable height for 100 times the 
height of the topographic feature (100 H) or 
2 miles (3.22 km), whichever is less. This distance 
shall be measured horizontally from the point at 
which the height H of the hill, ridge, or escarp- 
ment is determined; 

2. The hill, ridge, or escarpment protrudes above the 
height of upwind terrain features within a 2-mile 
(3.22-km) radius in any quadrant by a factor of 
two or more; 

3. The structure is located as shown in Figure 6-4 in 
the upper half of a hill or ridge or near the crest 
of an escarpment; 

4. H/L h > 0.2; and 



Minimum Design Loads for Buildings and Other Structures 



29 



5. H is greater than or equal to 15 ft (4.5 m) for 
Exposures C and D and 60 ft (18 m) for Expo- 
sure B. 

6.5.7.2 Topographic Factor. The wind speed-up effect 
shall be included in the calculation of design wind loads 
by using the factor K zt : 

K zt ^(l + K { K 2 K 3 f (Eq. 6-3) 

where K\, K 2 , and K$ are given in Figure 6-4. 

6.5.8 Gust Effect Factor. 

6.5.8.1 Rigid Structures. For rigid structures as defined 
in Section 6.2, the gust effect factor shall be taken as 
0.85 or calculated by the formula: 



h 



0.925 



c(33/z) 



(1 + l.WzQ ) 

l+ugvir 

1/6 



(Eq. 6-4) 
(Eq. 6-5) 



where /~ = the intensity of turbulence at height z where 
z = the equivalent height of the structure defined as 
0.6 h but not less than z m m for all building heights h. 
Zmin and c are listed for each exposure in Table 6-2; gg 
and g v shall be taken as 3.4. The background response 
Q is given by 



e = 



N 



i 



1 + 0.63 



fi + i 
~I7 



0.63 



(Eq. 6-6) 



where B, h are defined in Section 6.3; and Li = the 
integral length scale of turbulence at the equivalent 
height given by 

Li = l(I/33f (Eq. 6-7) 

in which I and e are constants listed in Table 6-2. 

6.5.8.2 Flexible or Dynamically Sensitive Structures. 

For flexible or dynamically sensitive structures as 
defined in Section 6.2, the gust effect factor shall be 
calculated by: 



'/ 



0.925 



\ + l.lh^Q 2 + g 2 R R 2 



\ 



1 + \Jg v k 



(Eq. 6-8) 



gQ and g v shall be taken as 3.4 and gn is given by 

0.577 



g* = V'21n(3600ni) + 



V21n(3600«i) 



(Eq. 6-9) 



7?, the resonant response factor, is given by 



R = J^R„R h R B (0.53 + 0A7R L ) 



R„ = 



7.47 N, 



(H-10.3iV,) 5 /3 



n i Lj 

Ri = -- ^(1 - e~ 2r >) for n > 
Rt - 1 for rj = 



(Eq. 6-10) 

(Eq. 6-11) 
(Eq. 6-12) 

(Eq, 6-13a) 
(Eq. 6-13b) 



where the subscript £ in Eq, 6-13 shall be taken as h, 
B, and L respectively where h, B, L are defined in 
Section 6.3. 

n\ = building natural frequency; 
R t = R h setting rj = 4.6n { h/V I ; 
Rf — R B setting t] — 4.6n\B/V z -; 
R. t = R L setting rj - 15 An [L/Vj; 
p = damping ratio, percent of critical; and 
Vj = mean hourly wind speed (ft/sec) at height z 
determined from Eq. 6-14. 



V T = b 



33 



V — 
,60 



(Eq. 6-14) 



where b and a are constants listed in Table 6-2 and V 
is the basic wind speed in mph. 

6.5.8.3 Rational Analysis. In lieu of the procedure 
defined in Sections 6.5.8.1 and 6.5.8.2, determination of 
the gust effect factor by any rational analysis defined in 
the recognized literature is permitted. 

6.5.8.4 Limitations. Where combined gust effect fac- 
tors and pressure coefficients (GC pj GC pi , and GC P f) 
are given in figures and tables, the gust effect factor shall 
not be determined separately. 

6.5.9 Enclosure Classifications., 



6.5.9.1 General. For the purpose of determining inter- 
nal pressure coefficients, all buildings shall be classified 
as enclosed, partially enclosed, or open as defined in 
Section 6.2. 



6.5.9.2 Openings. A determination shall be made of the 
amount of openings in the building envelope in order 
to determine the enclosure classification as defined in 
Section 6.5.9.1. 



30 



ASCE 7-02 



6.5.9.3 Wind-Borne Debris. Glazing in buildings clas- 
sified as Category II, III, or IV (Note 1) located in 
wind-borne debris regions shall be protected with an 
impact-resistant covering or be impact-resistant glaz- 
ing according to the requirements (Note 2) specified 
in Ref. 6-1 and Ref. 6-2 referenced therein or other 
approved test methods and performance criteria. 

Notes: 

1. In Category II, III, or IV buildings, glazing located 
over 60 ft (18.3 m) above the ground and over 
30 ft (9.2 m) above aggregate surface roof debris 
located within 1500 ft (458 m) of the building 
shall be permitted to be unprotected. 

Exceptions: In Category II and III buildings 
(other than health care, jail, and detention facil- 
ities, power generating and other public util- 
ity facilities), unprotected glazing shall be per- 
mitted, provided that unprotected glazing that 
receives positive external pressure is assumed 
to be an opening in determining the buildings' 
enclosure classification. 



Figure 6-5 based on building enclosure classifications 
determined from Section 6.5.9. 

6o5.ll.lJ Reduction Factor for Large Volume 
Buildings, Ri . For a partially enclosed building con- 
taining a single, unpartitioned large volume, the inter- 
nal pressure coefficient, GC pi , shall be multiplied by 
the following reduction factor, R t : 

R ( = 1.0 or 
/ 



R; = 0.5 



+ 



'1 + 



V t 



22, S00A og j 



< 1.0 



(Eq. 6-16) 



where 



\ og — total area of openings in the building 

envelope (walls and roof, in ft 2 ) 
Vt — unpartitioned internal volume, in ft 3 



6.5.11.2 External Pressure Coefficients. 



2. The levels of impact resistance shall be a function 
of Missile Levels and Wind Zones specified in 
Ref. 6-2. 

6*5.9.4 Multiple Classifications. If a building by def- 
inition complies with both the "open" and "partially 
enclosed" definitions, it shall be classified as an "open" 
building. A building that does not comply with either 
the "open" or "partially enclosed" definitions shall be 
classified as an "enclosed" building. 

6.5.10 Velocity Pressure. Velocity pressure, q z , evaluated 
at height z shall be calculated by the following equation: 

q z = 0.00256 K z K zt K d V 2 I (lb/ft 2 ) 

[In ST: q 7 = 0.613 K 7 K 7t K d V 2 l (N/m 2 ); V in m/s] 

(Eq. 6-15) 
where K d is the wind directionality factor defined in 
Section 6.5.4.4, K z is the velocity pressure exposure coef- 
ficient defined in Section 6.5.6.6 and K zt is the topographic 
factor defined in Section 6.5.7.2, and q\ x is the velocity pres- 
sure calculated using Eq. 6-15 at mean roof height h. 

The numerical coefficient 0.00256 (0.613 in SI) shall be 
used except where sufficient climatic data are available to 
justify the selection of a different value of this factor for a 
design application. 



6.5.11.2.1 Main Wind Force-Resisting Systems. 
External pressure coefficients for main wind force- 
resisting systems C p are given in Figures 6-6, 6-7, 
and 6-8. Combined gust effect factor and external 
pressure coefficients, GC P /, are given in Figure 6-10 
for low-rise buildings. The pressure coefficient val- 
ues and gust effect factor in Figure 6-10 shall not 
be separated. 

6.5.11.2.2 Components and Cladding. Combined 
gust effect factor and external pressure coefficients 
for components and cladding GC P are given in 
Figures 6-11 through 6-17. The pressure coefficient 
values and gust effect factor shall not be separated. 

6.5.113 Force Coefficients. Force coefficients Cf are 
given in Figures 6- 1 8 through 6-22. 

6.5.11.4 Roof Overhangs. 

6.5.11.4.1 Main Wind Force-Resisting System. 
Roof overhangs shall be designed for a positive 
pressure on the bottom surface of windward roof 
overhangs corresponding to C p — 0.8 in combination 
with the pressures determined from using Figures 6-6 
and 6-10. 



6.5.11 Pressure and Force Coefficients. 

6.5.11.1 Interna! Pressure Coefficient. Internal pres- 
sure coefficients, GC p i, shall be determined from 



6.5.11.4.2 Components and Cladding. For all build- 
ings, roof overhangs shall be designed for pres- 
sures determined from pressure coefficients given in 
Figure 6-1 IB, C, and D. 



Minimum Design Loads for Buildings and Other Structures 



31 



6.5.11.5 Parapets. 

6.5.11.5.1 Main Wind Force-Resisting System. The 
pressure coefficients for the effect of parapets on the 
MWFRS loads are given in Section 6.5.12.2,4 

6.5.11.5.2 Components and Cladding. The pres- 
sure coefficients for the design of parapet com- 
ponent and cladding elements are taken from the 
wall and roof pressure coefficients as specified in 
Section 6.5.12.4.4. 

6.5.12 Design Wind Loads on Enclosed and Partially 
Enclosed Buildings. 

6.5.12.1 General. 

6.5.12.1.1 Sign Convention. Positive pressure acts 
toward the surface and negative pressure acts away 
from the surface. 

6.5.12.1.2 Critical Load Condition. Values of exter- 
nal and internal pressures shall be combined alge- 
braically to determine the most critical load. 

6.5.12.1.3 Tributary Areas Greater Than 700 ft 2 
(65 m 2 ). Component and cladding elements with 
tributary areas greater than 700 ft 2 (65 m 2 ) shall be 
permitted to be designed using the provisions for main 
wind force resisting systems, 

6.5.12.2 Main Wind Force-Resisting Systems. 

6.5.12.2.1 Rigid Buildings of All Height. Design 
wind pressures for the main wind force-resisting 
system of buildings of all heights shall be determined 
by the following equation: 

p = qGC p ~~ qi(GC pi ) (lb/ft 2 ) (N/m 2 ) (Eq. 6-17) 



where 



q — q z for windward walls evaluated at height 
z above the ground; 

q — q h for leeward walls, side walls, and 
roofs, evaluated at height h; 

q } — q h for windward walls, side walls, 
leeward walls, and roofs of enclosed 
buildings and for negative internal 
pressure evaluation in partially 
enclosed buildings; 

qi = q z for positive internal pressure 

evaluation in partially enclosed buildings 
where height z is defined as the level of 
the highest opening in the building 



that could affect the positive internal 
pressure. For buildings sited in wind- 
borne debris regions, glazing that is not 
impact resistant or protected with an 
impact-resistant covering, shall be treated 
as an opening in accordance with 
Section 6.5.9.3. For positive internal 
pressure evaluation, q t may 
conservatively be evaluated at height 
h (q t - q h )\ 
G — gust effect factor from Section 6.5.8; 
C p = external pressure coefficient from 
Figure 6-6 or 6-8; 
(GCpi) = internal pressure coefficient from 
Figure 6-5 

q and q t shall be evaluated using exposure 
defined in Section 6.5.6.3. Pressure shall be applied 
simultaneously on windward and leeward walls and 
on roof surfaces as defined in Figures 6-6 and 6-8. 

6.5.12.2.2 Low-Rise Building. Alternatively, design 
wind pressures for the main wind force-resisting 
system of low-rise buildings shall be determined by 
the following equation: 

p - q h [(GC pf ) - (GC pi )] (lb/ft 2 )(N/m 2 ) 

(Eq. 6-18) 
where 

q h = velocity pressure evaluated at mean roof 

height h using exposure defined in 

Section 6.5.6.3; 
(GCpf) — external pressure coefficient from 

Figure 6-10; and 
(GC P i) — internal pressure coefficient from 

Figure 6-5. 

6.5.12.2.3 Flexible Buildings. Design wind pressures 
for the main wind force-resisting system of flexi- 
ble buildings shall be determined from the follow- 
ing equation: 

p = qG f Cp - qi(GC pi ) (lb/ft 2 ) (N/m 2 ) 

(Eq. 6-19) 
where q, q t , C p and (GC pi ) are as defined 
in Section 6.5.12.2.1 and, G^=gust effect factor 
defined in Section 6.5.8.2 

6.5.12.2.4 Parapets. The design wind pressure for 
the effect of parapets on main wind force-resisting 
systems of rigid, low-rise or flexible buildings with 
flat, gable, or hip roofs shall be determined by the 
following equation: 



p p - qpGCpn (Ib/sf) 



32 



(Eq. 6-20) 
ASCE 7-02 



where 

p p ~ combined net pressure on the parapet due 
to the combination of the net pressures 
from the front and back parapet surfaces. 
Plus (and minus) signs signify net pressure 
acting toward (and away from) the front 
(exterior) side of the parapet. 
q p =z velocity pressure evaluated at the top of 
the parapet. 
GC pn — combined net pressure coefficient 
= +1.8 for windward parapet 
— —1.1 for leeward parapet 



6.5.12.3 Design Wind Load Cases. The main wind 
force-resisting system of buildings of all heights, whose 
wind loads have been determined under the provisions 
of Sections 6.5.12.2.1 and 6.5.12.2.3, shall be designed 
for the wind load cases as defined in Figure 6-9. The 
eccentricity e for rigid structures shall be measured 
from the geometric center of the building face and shall 
be considered for each principal axis (ex, ey). The 
eccentricity e for flexible structures shall be determined 
from the following equation and shall be considered for 
each principal axis (ex, ey): 



e = 



where 



e Q + UIz V ^Qeo) 2 + (gR~R^) 2 



MIzVfgQQP + igRW 



(Eq. 6-21) 



eQ — eccentricity e as determined for 
rigid structures in Figure 6-9 
= distance between the elastic shear 
center and center of mass of each 
floor 
gQ, G> 8r, R shall be as defined in 
Section 6.5.8 



£r 



I 



The sign of the eccentricity e shall be plus or minus, 
whichever causes the more severe load effect. 



Exception: One-story buildings with h less than or 
equal to 30 ft, buildings two stories or less framed 
with light-framed construction and buildings two 
stories or less designed with flexible diaphragms need 
only be designed for Load Case 1 and Load Case 3 
in Figure 6-9. 

6.5.12.4 Components and Cladding. . 



p - q h [(GC p ) - (GC pi )] (lb/fr)(N/m 2 ) (Eq. 6-22) 

where 

q h — velocity pressure evaluated at mean roof 

height h using exposure defined in 

Section 6.5.6.3 
(GC P ) = external pressure coefficients given in 

Figures 6-11 through 6-16; and 
(GCpi) = internal pressure coefficient given in 

Figure 6-5. 

6.5.12.4.2 Buildings with h > 60 ft (18.3 m). 
Design wind pressures on components and cladding 
for all buildings with h > 60 ft (18.3 m) shall be 
determined from the following equation: 

p - q(GC p ) - qi(GC pi ) (lb/ft 2 ) (N/m 2 ) 



(Eq. 6-23) 



where 



q — q z for windward walls calculated at 
height z above the ground; 

q = q h for leeward walls, side walls, and 
roofs, evaluated at height h; 

q i = q fl for windward walls, side walls, 
leeward walls, and roofs of enclosed 
buildings and for negative internal 
pressure evaluation in partially enclosed 
buildings; and 

q { =z q z for positive internal pressure 

evaluation in partially enclosed buildings 
where height z is defined as the level of 
the highest opening in the building that 
could affect the positive internal pressure. 
For buildings sited in wind-borne debris 
regions, glazing that is not impact 
resistant or protected with an 
impact-resistant covering, shall be treated 
as an opening in accordance with 
Section 6.5.9.3. For positive internal 
pressure evaluation, q,- may 
conservatively be evaluated at height h 

(Qi = Qh)\ 
(GC P ) = external pressure coefficient from 

Figure 6-17; and 
(GCpi) = internal pressure coefficient given in 

Figure 6-5 

q and qi shall be evaluated using exposure defined in 
Section 6.5.6.3. 



6.5.12.4.1 Low-Rise Buildings and Buildings with 
h < 60 ft (183 m). Design wind pressures on compo- 
nent and cladding elements of low-rise buildings and 
buildings with h < 60 ft (18.3 m) shall be determined 
from the following equation: 



6.5,12.4,3 Alternative Design Wind Pressures for 
Components and Cladding in Buildings with 60 ft 
(18.3 m) < h < 90 ft (21 A m). Alternative to the 
requirements of Section 6.5.12.4.2, the design of 
components and cladding for buildings with a mean 



Minimum Design Loads for BuiSdsngs and Other Structures 



33 



roof height greater than 60 ft (18.3 m) and less than 
90 ft (27.4 m) values from Figure 6-11 through 6-17 
shall be used only if the height to width ratio is one 
or less (except as permitted by Note 6 of Figure 6-17) 
and Eq. 6-22 is used. 

6.5.12,4.4 Parapets. The design wind pressure on the 
components and cladding elements of parapets shall 
be designed by the following equation: 



METHOD 3 ■ 



SECTION 6.6 
■ WIND-TUNNEL PROCEDURE 



p = q p (GC p - GC P i) 



(Eq. 6-24) 



where 



q p — velocity pressure evaluated at the top of 

the parapet; 
GC P = external pressure coefficient from 

Figures 6-11 through 6-17; and 
GC pi — internal pressure coefficient from 

Figure 6-5, based on the porosity of the 

parapet envelope. 

Two load cases shall be considered. Load Case 
A shall consist of applying the applicable positive 
wall pressure from Figure 6-11 A or 6-17 to the front 
surface of the parapet while applying the applicable 
negative edge or corner zone roof pressure from 
Figure 6-1 IB through 6-17 to the back surface. Load 
Case B shall consist of applying the applicable 
positive wall pressure from Figure 6-11 A or 6-17 to 
the back of the parapet surface, and applying the 
applicable negative wall pressure from Figure 6-11 A 
or 6-17 to the front surface. Edge and corner zones 
shall be arranged as shown in Figures 6-11 through 
6-17. GC P shall be determined for appropriate roof 
angle and effective wind area from Figures 6-11 
through 6-17. If internal pressure is present, both load 
cases should be evaluated under positive and negative 
internal pressure. 

6.5.13 Design Wind Loads on Open Buildings and 
Other Structures. The design wind force for open build- 
ings and other structures shall be determined by the follow- 
ing formula: 



F = q z GC f A f (lb)(N) 



(Eq. 6-25) 



where 



q z = velocity pressure evaluated at height z of the 
centroid of area Af using exposure defined in 
Section 6.5.6.3; 
G — gust effect factor from Section 6.5.8; 
Cf = net force coefficients from Figure 6-18 through 

6-22; and 
Af — projected area normal to the wind except where Cf 
is specified for the actual surface area, ft 2 (m 2 ). 



6*6.1 Scope. Wind-tunnel tests shall be used where 
required by Section 6.5.2. Wind-tunnel testing shall be 
permitted in lieu of Methods 1 and 2 for any building 
or structure. 

6.6.2 Test Conditions. Wind-tunnel tests, or similar tests 
employing fluids other than air, used for the determina- 
tion of design wind loads for any building or other struc- 
ture, shall be conducted in accordance with this section. 
Tests for the determination of mean and fluctuating forces 
and pressures shall meet all of the following condi- 
tions: 

1. the natural atmospheric boundary layer has been 
modeled to account for the variation of wind speed 
with height; 

2. the relevant macro (integral) length and micro length 
scales of the longitudinal component of atmospheric 
turbulence are modeled to approximately the same 
scale as that used to model the building or structure; 

3. the modeled building or other structure and sur- 
rounding structures and topography are geometrically 
similar to their full-scale counterparts, except that, 
for low-rise buildings meeting the requirements of 
Section 6.5.1, tests shall be permitted for the mod- 
eled building in a single exposure site as defined in 
Section 6.5.6.3; 

4. the projected area of the modeled building or other 
structure and surroundings is less than 8% of the test 
section cross-sectional area unless correction is made 
for blockage: 

5. the longitudinal pressure gradient in the wind-tunnel 
test section is accounted for; 

6. Reynolds number effects on pressures and forces are 
minimized; and 

7. response characteristics of the wind-tunnel instrumen- 
tation are consistent with the required measurements. 

6.63 Dynamic Response. Tests for the purpose of deter- 
mining the dynamic response of a building or other structure 
shall be in accordance with Section 6.6.2. The structural 
model and associated analysis shall account for mass dis- 
tribution, stiffness, and damping. 

6.6.4 Limitations. 

6.6.4.1 Limitations on Wind Speeds. Variation of 
basic wind speeds with direction shall not be permit- 
ted unless the analysis for wind speeds conforms to the 
requirements of Section 6.5.4.2. 



34 



ASCE 7-02 



SECTION 6.7 
REFERENCES 

Ref. 6-1 Standard Test Method for Performance of Exte- 
rior Windows, Curtain Walls, Doors and Storm 
Shutters Impacted by Missile(s) and Exposed to 
Cyclic Pressure Differentials, ASTM El 886-97, 
ASTM Inc., West Conshohocken, PA, 1997. 

Ref. 6-2 Specification Standard for Performance of Exte- 
rior Windows, Glazed Curtain Walls, Doors and 
Storm Shutters Impacted by Windborne Debris in 
Hurricanes, ASTM E 1996-99, ASTM Inc., West 
Conshohocken. PA, 1999. 



Minimum Design Loads for Buildings and Other Structures 35 




FIGURE 6-1 
BASIC WIND SPEED 



36 



ASCE 7-02 




90(40) 
100(45) 



130(58) 
140(63) 



130(58) 
140(63) 

150(67) 



90(40) 
100(45) / 1130(58) 
110(49)120(54) 



Location 
Hawaii 
Puerto Rico 
Guam 

Virgin Islands 
American Samoa 



V mph (m/s) 
105 (47) 



145 
170 
145 
125 



(65) 
(76) 
(65) 
(56) 



Notes: 

1. Values are nominal design 3-second gust wind speeds in miles per hour (m/s) 
at 33 ft (10 m) above ground for Exposure C category. 

2. Linear interpolation between wind contours is permitted. 

3. Islands and coastal areas outside the last contour shall use the last wind speed 
contour of the coastal area. 

4. Mountainous terrain, gorges, ocean promontories, and special wind regions 
shall be examined for unusual wind conditions. 

FIGURE 6-1 — continued 
BASIC WIND SPEED 



Minimum Design Loads for Buildings and Other Structures 



37 



00 
00 




100(45) // 130(58) 
110(49)120(54) 



140(63) 150(67) 

Notes: 

1. Values are nominal design 3-second gust wind 
speeds in miles per hour (m/s) at 33 ft (10 m) 
above ground for Exposure C category. 
Linear interpolation between wind contours is 
permitted. 

Islands and coastal areas outside the last 
contour shall use the last wind speed contour 
of the coastal area. 
Mountainous terrain, gorges, ocean 
promontories, and special wand regions shall 
be examined for unusual wind conditions. 



> 

CO 
O 

m 



FIGURE 6-1a 
BASIC WIND SPEED - WESTERN GULF OF MEXICO HURRICANE COASTLINE 



o 



3 

C 

3 
o 

£2. 
cq" 

3 

r~ 

o 

» 



P3 



3 

CQ 
CO 

0) 
3 

a 



3" 
CD 



w 



90(40) 

100(45) 

110(49) 

120(54) 
130(58) 




130(58) 
140(63) 



Special Wind Region 



Notes: 

1. Values are nominal design 3-second gust wind 
speeds in miles per hour (mis) at 33 ft (10 m) 
above ground for Exposure C category. 

2. Linear interpolation between wind contours is 
permitted. 

3. Islands and coastal areas outside the last 
contour shall use the last wind speed contour 
of the coastal area. 

4. Mountainous terrain, gorges, ocean 
promontories, and special wind regions shall 
be examined for unusual wind conditions. 



150(67) 



FIGURE 6-1 b 
BASIC WIND SPEED - EASTERN GULF OF MEXICO AND SOUTHEASTERN US HURRICANE COASTLINE 



CO 




Special Wind Region 



Notes: 

1. Values are nominal design 3~second gust wind 
speeds in miles per hour (m/s) at 33 ft (10 m) 
above ground for Exposure C category 

2. Linear interpolation between wind contours is 
permitted. 

3- Islands and coastal areas outside the last 
contour shall use the last wind speed contour 
of the coastal area. 

4 Mountainous terrain, gorges, ocean 
promontories, and special wind regions shall 
be examined for unusual wind conditions. 



FIGURE 6-1c 
BASIC WIND SPEED - MID AND NORTHERN ATLANTIC HURRICANE COASTLINE 



Main Wind Force Resisting System - Method 1 



Si < 60 ft. 



Figure 6-2 



Design Wind Pressures 



Enclosed Buildings 



Walls & Roofs 




Transverse 



Notes: 
1 



10. 



Pressures shown are applied to the horizontal and vertical projections, for exposure B, at h=30 ft (9. lm), for 1=1 .0. Adjust to other 

exposures and heights with adjustment factor X. 

The load patterns shown shall be applied to each corner of the building in turn as the reference corner. (See Figure 6-10) 

For the design of the longitudinal MWFRS use — 0°, and locate the zone E/F, G/H boundary at the mid-length of the building. 

Load cases 1 and 2 must be checked for 25° < 9 < 45°. Load case 2 at 25° is provided only for interpolation between 25° to 30°. 

Plus and minus signs signify pressures acting toward and away from the projected surfaces, respectively. 

For roof slopes other than those shown, linear interpolation is permitted. 

The total horizontal load shall not be less than that determined by assuming ps = in zones B & D. 

The zone pressures represent the following: 

Horizontal pressure zones - Sum of the windward and leeward net (sum of internal and external) pressures on vertical projection of: 

A- End zone of wall C- Interior zone of wall 

B - End zone of roof D - Interior zone of roof 

Vertical pressure zones - Net (sum of internal and external) pressures on horizontal projection of: 

E - End zone of windward roof G - Interior zone of windward roof 

F- End zone of leeward roof H- Interior zone of leeward roof 

Where zone E or G falls on a roof overhang on the windward side of the building, use Eoh and Goh for the pressure on the horizontal 
projection of the overhang. Overhangs on the leeward and side edges shall have the basic zone pressure applied. 
Notation: 
a: 1 percent of least horizontal dimension or 0.4h, whichever is smaller, but not less than either 4% of least horizontal dimension 

or 3 ft (0.9 m). 
h: Mean roof height, in feet (meters), except that eave height shall be used for roof angles <10°. 
0: Angle of plane of roof from horizontal, in degrees. 



Minimum Design Loads for Buildings and Other Structures 



41 



Main Wind Force Resisting System - Method 1 


h < 60 ft 


Figure 6-2 (cont'd) j Design Wind Pressures 


Walls & Roofs 


Enclosed Buildings 




Simplified Design Wind Pressure , p S 3o (psf) (Exposure Bath = 30 ft. with I = 1.0) 






Basic Wind 
Speed 
(mph) 


Roof 

Angle 

(degrees) 



</> 

U 

O 

_l 


Zones 




Horizontal Pressures 


Vertical Pressures 


Overhangs 


A 


B 


C 


D 


E 


F 


G 


H 


EOH 


GOH 


85 


0to5° 




11.5 


-5.9 


7.6 


-3.5 


-13.8 


-7.8 


-9.6 


-6.1 


-19.3 


-15.1 


10° 




12.9 


-5.4 


8.6 


-3.1 


-13.8 


-8.4 


-9.6 


-6.5 


-19.3 


-15.1 


15° 




14.4 


-4.8 


9.6 


-2.7 


-13.8 


-9.0 


-9.6 


-6.9 


-19.3. 


-15.1 


20° 




15.9 


-4.2 


10.6 


-2.3 


-13.8 


-9.6 


-9.6 


-7.3 


-19.3 


-15.1 


25° 




14.4 


2.3 


10.4 


2.4 


-6.4 
-2.4 


-8.7 
-4.7 


-4.6 
-0.7 


-7.0 
-3.0 


-11.9 


-10.1 


30 to 45 




12.9 
12.9 


8.8 
8.8 


10.2 
10.2 


7.0 
7.0 


1.0 
5.0 


-7.8 
-3.9 


0.3 
4.3 


-6.7 
-2.8 


-4.5 
-4.5 


-5.2 
-5.2 


90 


0to5° 




12.8 


-6.7 


8.5 


-4.0 


-15.4 


-8.8 


-10.7 


-6.8 


-21.6 


-16.9 


10° 




14.5 


-6.0 


9.6 


-3.5 


-15.4 


-9.4 


-10.7 


-7.2 


-21.6 


-16.9 


15° 




16.1 


-5.4 


10.7 


-3.0 


-15.4 


-10.1 


-10.7 


-7.7 


-21.6 


-16.9 


20° 




17.8 


-4.7 


11.9 


-2.6 


-15.4 


-10.7 


-10.7 


-8.1 


-21.6 


-16.9 


25° 




16.1 


2.6 


11.7 


2.7 


-7.2 
-2.7 


-9.8 
-5.3 


-5.2 
-0.7 


-7.8 
-3.4 


-13.3 


-11.4 


30 to 45 




14.4 
14.4 


9.9 
9.9 


11.5 
11.5 


7.9 
7.9 


1.1 
5.6 


-8.8 
-4.3 


0.4 
4.8 


-7.5 
-3.1 


-5.1 
-5.1 


-5.8 
-5.8 


100 


0to5° 




15.9 


-8.2 


10.5 


-4.9 


-19.1 


-10.8 


-13.3 


-8.4 


-26.7 


-20.9 


10° 




17.9 


-7.4 


11.9 


^.3 


-19.1 


-11.6 


-13.3 


-8.9 


-26.7 


-20.9 


15° 




19.9 


-6.6 


13.3 


-3.8 


-19.1 


-12.4 


-13.3 


-9.5 


-26.7 


-20.9 


20° 




22.0 


-5.8 


14.6 


-3.2 


-19.1 


-13.3 


-13.3 


-10.1 


-26.7 


-20.9 


25° 




19.9 


3.2 


14.4 


3.3 


-8.8 
-3.4 


-12.0 
-6.6 


-6.4 
-0.9 


-9.7 
-4.2 


-16.5 


-14.0 


30 to 45 




17.8 
17.8 


12.2 
12.2 


14.2 
14.2 


9.8 
9.8 


1.4 
6.9 


-10.8 
-5.3 


0.5 
5.9 


-9.3 
-3.8 


-6.3 
-6.3 


-7.2 
-7.2 


110 


0to5° 




19.2 


-10.0 


12.7 


-5.9 


-23.1 


-13.1 


-16.0 


-10.1 


-32.3 


-25.3 


10° 




21.6 


-9.0 


14.4 


-5.2 


-23.1 


-14.1 


-16.0 


-10.8 


-32.3 


-25.3 


15° 




24.1 


-8.0 


16.0 


-4.6 


-23.1 


-15.1 


-16.0 


-11.5 


-32.3 


-25.3 


20° 




26.6 


-7.0 


17.7 


-3.9 


-23.1 


-16.0 


-16.0 


-12.2 


-32.3 


-25.3 


25° 




24.1 


3.9 


17.4 


4.0 


-10.7 
-4.1 


-14.6 
-7.9 


-7.7 
-1.1 


-11.7 
-5.1 


-19.9 


-17.0 


30 to 45 




21.6 
21.6 


14.8 
14.8 


17.2 
17.2 


11.8 
11.8 


1.7 
8.3 


-13.1 
-6.5 


0.6 
7.2 


-11.3 
-4.6 


-7.6 
-7.6 


-8.7 
-8.7 


120 


0to5° 




22.8 


-11.9 ^ 


15.1 


-7.0 


-27.4 


-15.6 


-19.1 


-12.1 


-38.4 


-30.1 


10° 




25.8 


-10.7 


17.1 


-6.2 


-27.4 


-16.8 


-19.1 


-12.9 


-38.4 


-30.1 


15° 




28.7 


-9.5 


19.1 


-5.4 


-27.4 


-17.9 


-19.1 


-13.7 


-38.4 


-30.1 


20° 




31.6 


-8.3 


21.1 


-4.6 


-27.4 


-19.1 


-19.1 


-14.5 


-38.4 


-30.1 


25° 




28.6 


4.6 


20.7 


4.7 


-12.7 
-4.8 


-17.3 
-9.4 


-9.2 
-1.3 


-13.9 
-6.0 


-23.7 


-20.2 


30 to 45 




25.7 
25.7 


17.6 
17.6 


20.4 
20.4 


14.0 
14.0 


2.0 
9.9 


-15.6 
-7.7 


0.7 
8,6 


-13.4 
-5.5 


-9.0 
-9.0 


-10.3 
-10.3 


130 


to 5° 




26.8 


-13.9 


17.8 


-8.2 


-32.2 


-18.3 


-22.4 


-14.2 


-45.1 


-35.3 


10° 




30.2 


-12.5 


20.1 


-7.3 


-32.2 


-19.7 


-22.4 


-15.1 


-45.1 


-35.3 


15° 




33.7 


-11.2 


22.4 


-6.4 


-32.2 


-21.0 


-22.4 


-16.1 


-45.1 


-35.3 


20° 




37.1 


-9.8 


24.7 


-5.4 


-32.2 


-22.4 


-22.4 


-17.0 


-45.1 


-35.3 


25° 


2 


33.6 


5.4 


24.3 


5.5 


-14.9 
-5.7 


-20.4 
-11.1 


-10.8 
-1.5 


-16.4 
-7.1 


-27.8 


-23.7 


30 to 45 


1 
2 


30.1 
30.1 


20.6 
20.6 


24.0 
24.0 


16.5 
16.5 


2.3 
11.6 


-18.3 
-9.0 


0.8 
10.0 


-15.7 
-6.4 


-10.6 
-10.6 


-12.1 
-12.1 




Unit Conversions - 1,0 ft = 03048 i 


b; 1.0 psf = 0.0479 kN/m 2 







42 



ASCE 7-02 



Main Wind Force Resisting System - Method 1 



h < 60 ft 



Figure 6-2 (cont'd) | Design Wind Pressures 



Enclosed Buildings 



Walls & Roofs 



Simplified Design Wind Pressure 


> PS30 


[psf) (Exposure 


Bath = 


30 ft. with 1 = 1.0) 


Basic Wind 
Speed 
(mph) 


Roof 

Angle 

(degrees) 


to 

CO 

o 

"D 
CD 
O 

_l 


Zones 


Horizontal Pressures 


Vertical Pressures 


Overhangs 


A 


B 


C 


D 


E 


F 


G 


H 


Eoh 


Goh 


140 


0to5° 




31.1 


-16.1 


20.6 


-9.6 


-37.3 


-21.2 


-26.0 


-16.4 


-52.3 


-40.9 


10° 




35.1 


-14.5 


23.3 


-8.5 


-37.3 


-22.8 


-26.0 


-17.5 


-52.3 


-40.9 


15° 




39.0 


-12.9 


26.0 


-7.4 


-37.3 


-24.4 


-26.0 


-18.6 


-52.3 


^0.9 


20° 




43.0 


-11.4 


28.7 


-6.3 


-37.3 


-26.0 


-26.0 


-19.7 


-52.3 


-40.9 


25° 




39.0 


6.3 


28.2 


6.4 


-17.3 
-6.6 


-23.6 
-12.8 


-12.5 
-1.8 


-19.0 
-8.2 


-32.3 


-27.5 


30 to 45 




35.0 
35.0 


23.9 
23.9 


27.8 
27.8 


19.1 
19.1 


2.7 
13.4 


-21.2 
-10.5 


0.9 
11.7 


-18.2 
-7.5 


-12.3 
-12.3 


-14.0 
-14.0 


150 


0to5° 




35.7 


-18.5 


23.7 


-11.0 


-42.9 


-24.4 


-29.8 


-18.9 


-60.0 


-47.0 


10° 




40.2 


-16.7 


26.8 


-9.7 


-42.9 


-26.2 


-29.8 


-20.1 


-60.0 


-47.0 


15° 




44.8 


-14.9 


29.8 


-8.5 


-42.9 


-28.0 


-29.8 


-21.4 


-60.0 


-47.0 


20° 




49.4 


-13.0 


32.9 


-7.2 


-42.9 


-29.8 


-29.8 


-22.6 


-60.0 


-47.0 


25° 




44.8 


7.2 


32.4 


7.4 


-19.9 
-7.5 


-27.1 
-14.7 


-14.4 
-2.1 


-21.8 
-9.4 


-37.0 


-31.6 


30 to 45 




40.1 
40.1 


27.4 
27.4 


31.9 
31.9 


22.0 
22.0 


3.1 
15.4 


-24.4 
-12.0 


1.0 
13.4 


-20.9 
-8.6 


-14.1 
-14.1 


-16.1 
-16.1 


170 


0to5° 




45.8 


-23.8 


30.4 


-14.1 


-55.1 


-31.3 


-38.3 


-24.2 


-77.1 


-60.4 


10° 




51.7 


-21.4 


34.4 


-12.5 


-55.1 


-33.6 


-38.3 


-25.8 


-77.1 


-60.4 


15* 




57.6 


-19.1 


38.3 


-10.9 


-55.1 


-36.0 


-38.3 


-27.5 


-77.1 


-60.4 


20° 




63.4 


-16.7 


42.3 


-9.3 


-55.1 


-38.3 


-38.3 


-29.1 


-77.1 


-60.4 


25° 


2 


57.5 


9.3 


41.6 


9.5 


-25.6 
-9.7 


-34.8 
-18.9 


-18.5 
-2.6 


-28.0 
-12.1 


-47.6 


-40.5 


30 to 45 


1 
2 


51.5 
51.5 


35.2 
35.2 


41.0 
41.0 


28.2 
28.2 


4.0 
19.8 


-31.3 
-15.4 


1.3 
17.2 


-26.9 
-11.0 


-18.1 
-18.1 


-20.7 
-20.7 



Adjustment Factor 
for Building Height and Exposure, X 



Mean roof 
heiqht (fl} 


Exposure 


B 


c 


D 


15 


1.00 


1.21 


1.47 


20 


1.00 


1.29 


1.55 


25 


1.00 


1.35 


1.61 


30 


1.00 


1.40 


1.66 


35 


1.05 


1.45 


1.70 


40 


1.09 


1.49 


1.74 


45 


1.12 


1.53 


1.78 


50 


1.16 


1.56 


1.81 


55 


1.19 


1.59 


1.84 


60 


122 


1.62 


1.87 



Unit Conversions - 1.0 ft = 03048 m; 1.0 psf = 0.0479 kN/m 2 



Minimum Design Loads for Buildings and Other Structures 



43 



Components and Cladding -Method 1 



h < 60 ft 



Figure 6-3 



I 



Design Wind Pressures 



Enclosed Buildings 



Walls & Roofs 




Notes 



Flat Roof 




Hip Roof (7° < 6 < 27°) 





Gabie Roof (9 < 7°) 



Gable Roof (7° < 9 < 45°) 



□ 



Interior Zones 

Roofs - Zone 1 / Wails - Zone 4 



End Zones 

Roofs -Zone 2 /Walls -Zone 5 



Corner Zones 

Roofs -Zone 3 



1 . Pressures shown are applied normal to the surface, for exposure B, at h=30 ft (9. lm), for 1-1 .0. Adjust to other exposures and 
heights with adjustment factor X. 

2. Plus and minus signs signify pressures acting toward and away from the surfaces, respectively. 

3 . For hip roofs with 9 < 25°, Zone 3 shall be treated as Zone 2. 

4. For effective wind areas between those given, value may be interpolated, otherwise use the value associated with the lower 
effective wind area. 

5. Notation: 

a: 1 percent of least horizontal dimension or 0.4h, whichever is smaller, but not less than either 4% of least horizontal 

dimension or 3 ft (0.9 m). 
h: Mean roof height, in feet (meters), except that eave height shall be used for roof angles <10°. 
6: Angle of plane of roof from horizontal, in degrees. 



44 



ASCE 7-02 



^orhpniionts and Cladding - Method I 



Figure 6-3 (cont'd) | Design Wind Pressures 



h £ 60 ft. 



Enclosed Buildings 



Walls & Roofs 









Net Design Wind Pressure 


Pnet30 (P s fl (Exposure Bath 


= 30 ft. with 1 = 1.0) 










Zone 


Effective 

wind area 

(si) 


Basic Wind Speed V (mph) 


85 


90 


100 


110 


120 


130 


140 


150 


170 


(A 
<!> 

e> 
o> 

<b 
•a 

O 

© 

o 
o 


1 


10 


5.3 


-13.0 


5.9 


-14.6 


7.3 


-18.0 


8.9 


-21.8 


10.5 


-25.9 


12.4 


-30.4 


14.3 


-35.3 


16.5 


-40.5 


21.1 


-52.0 


1 


20 


5.0 


-12.7 


5.6 


-14.2 


6.9 


-17.5 


8.3 


-21.2 


9.9 


-25.2 


11.6 


-29.6 


13.4 


-34.4 


15.4 


-39.4 


19.8 


-50.7 


1 


50 


4.5 


-12.2 


5.1 


-13.7 


6.3 


-16.9 


7.6 


-20.5 


9.0 


-24.4 


10.6 


-28.6 


12.3 


-33.2 


14.1 


-38.1 


18.1 


-48.9 


1 


100 


4.2 


-11,9 


4.7 


-13.3 


5.8 


-16.5 


7.0 


-19.9 


8.3 


-23.7 


9.8 


-27.8 


11.4 


-32.3 


13.0 


-37.0 


16.7 


-47.6 


2 


10 


5.3 


-21.8 


5.9 


-24.4 


7.3 


-30.2 


8.9 


-36.5 


10.5 


-43.5 


12.4 


-51.0 


14.3 


-59.2 


16.5 


-67.9 


21.1 


-87.2 


2 


20 


5.0 


-19.5 


5.6 


-21.8 


6.9 


-27.0 


8.3 


-32.6 


9.9 


-38.8 


11.6 


■45.6 


13.4 


-52.9 


15.4 


-60.7 


19.8 


-78.0 


2 


50 


4.5 


-16.4 


5.1 


-18.4 


6.3 


-22.7 


7.6 


-27.5 


9.0 


-32.7 


10.6 


-38.4 


12.3 


■44.5 


14.1 


-51.1 


18.1 


-65.7 


2 


100 


4.2 


-14.1 


4.7 


-15.8 


5.8 


-19.5 


7.0 


-23.6 


8.3 


-28.1 


9.8 


-33.0 


11.4 


-38.2 


13.0 


-43.9 


16.7 


-564 


3 


10 


5.3 


-32.8 


5.9 


-36.8 


7.3 


-45.4 


8.9 


-55.0 


10.5 


-65.4 


12.4 


-76.8 


14.3 


-89.0 


16.5 


-102.2 


21.1 


-131.3 


3 


20 


5.0 


-27.2 


5.6 


-30.5 


6.9 


-37.6 


8.3 


-45.5 


9.9 


-54.2 


11.6 


-63.6 


13.4 


-73.8 


15.4 


-84.7 


19.8 


-108.7 


3 


50 


4.5 


-19.7 


5.1 


-22.1 


6.3 


-27.3 


7.6 


-33.1 


9.0 


-39.3 


10.6 


-46.2 


12.3 


-53.5 


14.1 


-61.5 


18.1 


-78.9 


3 


100 


4.2 


-14.1 


4.7 


-15.8 


5.8 


-19.5 


7.0 


-23.6 


8.3 


-28.1 


9.8 


-33.0 


11.4 


-38.2 


13.0 


-43.9 


16.7 


-56.4 


(0 
V 

a> 

CM 

O 
f- 
A 
O 


1 


10 


7.5 


-11.9 


8.4 


-13.3 


10.4 


-16.5 


12.5 


-19.9 


14.9 


-23.7 


17.5 


-27.8 


20.3 


-32.3 


23.3 


-37.0 


30.0 


-47.6 


1 


20 


6.8 


-11.6 


7.7 


-13.0 


9.4 


-16.0 


11.4 


-19.4 


13.6 


-23.0 


16.0 


-27.0 


18.5 


-31.4 


21.3 


-36.0 


27.3 


-46.3 


1 


50 


6.0 


-11.1 


6.7 


-12.5 


8.2 


-15.4 


10.0 


-18.6 


11.9 


-22.2 


13.9 


-26.0 


16.1 


-30.2 


18.5 


-34.6 


23.8 


-44.5 


1 


100 


5.3 


-10.8 


5.9 


-12.1 


7.3 


-14.9 


8.9 


-18.1 


10.5 


-21.5 


12.4 


-25.2 


14.3 


-29.3 


16.5 


-33.6 


21.1 


-43.2 


2 


10 


7.5 


-20.7 


8.4 


-23.2 


10.4 


-28.7 


12.5 


-34.7 


14.9 


-41.3 


17.5 


-48.4 


20.3 


-56.2 


23.3 


-64.5 


30.0 


-82.8 


2 


20 


6.8 


-19.0 


7.7 


-21.4 


9.4 


-26.4 


11.4 


-31.9 


13.6 


-38.0 


16.0 


-44.6 


18.5 


-51.7 


21.3 


-59.3 


27.3 


-76.2 


2 


50 


6.0 


-16.9 


6.7 


-18.9 


8.2 


-23.3 


10.0 


-28.2 


11.9 


-33.6 


13.9 


-39.4 


16.1 


-45.7 


18.5 


-52.5 


23.8 


-67.4 


2 


100 


5.3 


-15.2 


5.9 


-17.0 


7.3 


-21.0 


8.9 


-25.5 


10.5 


-30.3 


12.4 


-35.6 


14.3 


-41.2 


16.5 


-47.3 


21.1 


-60.8 


3 


10 


7.5 


-30.6 


8.4 


-34.3 


10.4 


-42.4 


12.5 


-51.3 


14.9 


-61.0 


17.5 


-71.6 


20.3 


-83.1 


23.3 


-95.4 


30.0 


-122.5 


3 


20 


6.8 


-28.6 


7.7 


-32.1 


9.4 


-39.6 


11.4 


-47.9 


13.6 


-57.1 


16.0 


-67.0 


18.5 


-77.7 


21.3 


-89.2 


27.3 


-114.5 


3 


50 


6.0 


-26.0 


6.7 


-29.1 


8.2 


-36.0 


10.0 


-43.5 


11.9 


-51.8 


13.9 


-60.8 


16.1 


-70.5 


18.5 


-81.0 


23.8 


-104.0 


3 


100 


5.3 


-24.0 


5.9 


-26.9 


^ULj 


-33.2 


8.9 


-40.2 


10.5 


-47.9 


12.4 


-56.2 


14.3 


-65.1 


16.5 


-74.8 


21.1 


-96.0 


« 

a> 

O) 

a> 
T3 

IO 

sr 

o 

CM 
A 

O 
O 
DC 


1 


10 


11.9 


-13.0 


13.3 


-14.6 


16.5 


-18.0 


19.9 


-21.8 


23.7 


-25.9 


27.8 


-30.4 


32.3 


-35.3 


37.0 


-40.5 


47.6 


-52.0 


1 


20 


11.6 


-12.3 


13.0 


-13.8 


16.0 


-17.1 


19.4 


-20.7 


23.0 


-24.6 


27.0 


-28.9 


31.4 


-33.5 


36.0 


-38.4 


46.3 


-49.3 


1 


50 


11.1 


-11.5 


12.5 


-12.8 


15.4 


-15.9 


18.6 


-19.2 


22.2 


-22.8 


26.0 


-26.8 


30.2 


-31.1 


34.6 


-35.7 


44.5 


-45.8 


1 


100 


10.8 


-10.8 


12.1 


-12.1 


14.9 


-14.9 


18.1 


-18.1 


21.5 


-21.5 


25.2 


-25.2 


29.3 


-29.3 


33.6 


-33.6 


43.2 


-43.2 


2 


10 


11.9 


-15.2 


13.3 


-17.0 


16.5 


-21.0 


19.9 


-25.5 


23.7 


-30.3 


27.8 


-35.6 


32.3 


41.2 


37.0 


^7.3 


47.6 


-60.8 


2 


20 


11.6 


-14.5 


13.0 


-16.3 


16.0 


-20.1 


19.4 


-24.3 


23.0 


-29.0 


27.0 


-34.0 


31.4 


-39.4 


36.0 


-45.3 


46.3 


-58.1 


2 


50 


11.1 


-13.7 


12.5 


-15.3 


15.4 


-18.9 


18.6 


-22.9 


22.2 


-27.2 


26.0 


-32.0 


30.2 


-37.1 


34.6 


-42.5 


44.5 


-54.6 


2 


100 


10.8 


-13.0 


12.1 


-14.6 


14.9 


-18.0 


18.1 


-21.8 


21.5 


-25.9 


25.2 


-30.4 


29.3 


-35.3 


33.6 


-40.5 


43.2 


-52.0 


3 


10 


11.9 


-15.2 


13.3 


-17.0 


16.5 


-21.0 


19.9 


-25.5 


23.7 


-30.3 


27.8 


-35.6 


32.3 


-41.2 


37.0 


-47.3 


47.6 


-60.8 


3 


20 


11.6 


-14.5 


13.0 


-16.3 


16.0 


-20.1 


19.4 


-24.3 


23.0 


-29.0 


27.0 


-34.0 


31.4 


-39.4 


36.0 


-45.3 


46.3 


-58.1 


3 


50 


11.1 


-13.7 


12.5 


-15.3 


15.4 


-18.9 


18.6 


-22.9 


22.2 


-27.2 


26.0 


-32.0 


30.2 


-37.1 


34.6 


^2.5 


44.5 


-54.6 


3 


100 


10.8 


-13.0 


12.1 


-14.6 


14.9 


-18.0 


18.1 


-21.8 


21.5 


-25.9 


25.2 


-30.4 


29.3 


-35.3 


33.6 


-40.5 


43.2 


-52.0 


13 
5 


4 


10 


13.0 


-14.1 


14.6 


-15.8 


18.0 


-19.5 


21.8 


-23.6 


25.9 


-28.1 


30.4 


-33.0 


35.3 


-38.2 


40.5 


-43.9 


52.0 


-56.4 


4 


20 


12.4 


-13.5 


13.9 


-15.1 


17.2 


-18.7 


20.8 


-22.6 


24.7 


-26.9 


29.0 


-31.6 


33.7 


-36.7 


38.7 


-42.1 


49.6 


-54.1 


4 


50 


11.6 


-12.7 


13.0 


-14.3 


16.1 


-17.6 


19.5 


-21.3 


23.2 


-25.4 


27.2 


-29.8 


31.6 


-34.6 


36.2 


-39.7 


46.6 


-51.0 


4 


100 


11.1 


-12.2 


12.4 


-13.6 


15.3 


-16.8 


18.5 


-20.4 


22.0 


-24.2 


25.9 


-28.4 


30.0 


-33.0 


34.4 


-37.8 


44.2 


-48.6 


4 


500 


9.7 


-10.8 


10.9 


-12.1 


13.4 


-14.9 


16.2 


-18.1 


19.3 


-21.5 


22.7 


-25.2 


26.3 


-29.3 


30.2 


-33.6 


38.8 


-43.2 


5 


10 


13.0 


-17.4 


14.6 


-19.5 


18.0 


-24.1 


21.8 


-29.1 


25.9 


-34.7 


30.4 


-40.7 


35.3 


-47.2 


40.5 


-54.2 


52.0 


-69.6 


5 


20 


12.4 


-16.2 


13.9 


-18.2 


17.2 


-22.5 


20.8 


-27.2 


24.7 


-32.4 


29.0 


-38.0 


33.7 


-44.0 


38.7 


-50.5 


49.6 


-64.9 


5 


50 


11.6 


-14.7 


13.0 


-16.5 


16.1 


-20.3 


19.5 


-24.6 


23.2 


-29.3 


27.2 


-34.3 


31.6 


-39.8 


36.2 


^5.7 


46.6 


-58.7 


5 


100 


11.1 


-13.5 


12.4 


-15.1 


15.3 


-18.7 


18.5 


-22.6 


22.0 


-26.9 


25.9 


-31.6 


30.0 


-36.7 


34.4 


^2.1 


44.2 


-54.1 


5 


500 


9.7 


-10.8 


10.9 


-12.1 


13.4 


-14.9 


16.2 


-18.1 


19.3 


-21.5 


22.7 


-25.2 


26.3 


-29.3 


30.2 


-33.6 


38.8 


-43.2 



Unit Conversions - 1.0 ft = 0.3048 m; 1.0 sf = 0.0929 m 2 ; 1.0 psf = 0.0479 kN/ni 2 



Minimum Design Loads for Buildings and Other Structures 



45 



^^^^p^l^^l^BH^^^II^l^ll^^j 



Figure 6-3 (cont'd) | Design Wind Pressures 



h < 60 ft 



Enclosed Buildings 



Walls & Roofs 



Roof Overhang Net Design Wind Pressure , p net 3o (psf) 
(Exposure Bath = 30 ft. with 1=1.0) 





Zone 


Effective 

Wind Area 

(sf) 


Basic Wind Speed V (mph) 


00 


100 


110 


120 


130 


140 


150 


170 


CO 

1 

h- 
o 

o 

o 
o 

IK 


2 


10 


-21.0 


-25.9 


-31.4 


-37,3 


-43.8 


-50.8 


-58.3 


-74.9 


2 


20 


-20.6 


-25.5 


-30.8 


-36.7 


-43.0 


-49.9 


-57.3 


-73.6 


2 


50 


-20.1 


-24.9 


-30.1 


-35.8 


-42.0 


-48.7 


-55.9 


-71.8 


2 


100 


-19.8 


-24.4 


-29.5 


-35.1 


-41.2 


-47.8 


-54.9 


-70.5 


3 


10 


-34.6 


-42.7 


-51.6 


-61.5 


-72.1 


-83.7 


-96.0 


-123.4 


3 


20 


-27.1 


-33.5 


-40.5 


-48.3 


-56.6 


-65.7 


-75.4 


-96.8 


3 


50 


-17.3 


-21.4 


-25.9 


-30.8 


-36.1 


-41.9 


-48.1 


-61.8 


3 


100 


-10.0 


-12.2 


-14.8 


-17.6 


-20.6 


-23.9 


-27.4 


-35.2 


W 
Q 
g) 

m 

0) 
•D 
N. 
tN 

o 

A 

o 
o 
0£ 


2 


10 


-27.2 


-33.5 


-40.6 


-48.3 


-56.7 


-65.7 


-75.5 


-96.9 


2 


20 


-27.2 


-33.5 


-40.6 


-48.3 


-56.7 


-65.7 


-75.5 


-96.9 


2 


50 


-27.2 


-33.5 


-40.6 


-48.3 


-56.7 


-65.7 


-75.5 


-96.9 


2 


100 


-27.2 


-33.5 


-40.6 


-48.3 


-56.7 


-65.7 


-75.5 


-96.9 


3 


10 


-45.7 


-56.4 


-68.3 


-81.2 


-95.3 


-110.6 


-126.9 


-163.0 


3 


20 


-41.2 


-50.9 


-61.6 


-73.3 


-86.0 


-99.8 


-114.5 


-147.1 


3 


50 


-35.3 


-43.6 


-52.8 


-62.8 


-73.7 


-85.5 


-98.1 


-126.1 


3 


100 


-30.9 


-38.1 


-46.1 


-54.9 


-64.4 


-74.7 


-85.8 


-110.1 


« 

o» 

a> 
■Q 
%n 

o 

h- 
tN 
A 

O 
O 


2 


10 


-24.7 


-30.5 


-36.9 


-43.9 


-51.5 


-59.8™ 1 


-68.6 


-88.1 


2 


20 


-24.0 


-29.6 


-35.8 


-42.6 


-50.0 


-58.0 


-66.5 


-85.5 


2 


50 


-23.0 


-28.4 


-34.3 


^0.8 


-47.9 


-55.6 


-63.8 


-82.0 


2 


100 


-22.2 


-27.4 


-33.2 


-39.5 


-46.4 


-53.8 


-61.7 


-79.3 


3 


10 


-24.7 


-30.5 


-36.9 


-43.9 


-51.5 


-59.8 


-68.6 


-88.1 


3 


20 


-24.0 


-29.6 


-35.8 


-42.6 


-50.0 


-58.0 


-66.5 


-85.5 


3 


50 


-23.0 


-28.4 


-34.3 


-40.8 


-47.9 


-55.6 


-63.8 


-82.0 


3 


100 


-22.2 


-27.4 


-33.2 


-39.5 


-46.4 


-53.8 


-61.7 


-79.3 



Adjustment Factor 
for Building Height and Exposure, X 



Mean roof 
heiaht (ft) 


Exposure 


B 


c 


D 


15 


1.00 


1.21 


1.47 


20 


1.00 


1.29 


1.55 


25 


1.00 


1.35 


1.61 


30 


1.00 


1.40 


1.66 


35 


1.05 


1.45 


1.70 


40 


1.09 


1.49 


1.74 


45 


1.12 


1.53 


1 7Q 


50 


1.16 


1.56 


1.81 


55 


1.19 


1.59 


1.84 


60 


1.22 


1.62 


1.87 



Unit Conversions - 1.0 ft = 03048 m; 1.0 sf = 0.0929 m 2 ; 1.0 psf = 0.0479 kN/m 2 



46 



ASCE 7-02 



Topographic Factor, K zt - Method 2 



Figure 6-4 




Speed-up 
s(Dowitwiad) 



m 



m 







Speed-up 
x (Downwind) 



E/2 



m 



-H 



ESCmPMEUl 



2*D RIDGE OR 3*D AXISYilETRICAL HILL 



Topographic Multipliers for Exposure C 


H/L h 


Kj Multiplier 


x/L h 


K 2 Multiplier 


z/L h 


K 3 Multiplier 


2-D 
Ridge 


2-D 
Escarp. 


3-D 
Axisym. 

Hill 


2-D 
Escarp. 


All 
Other 
Cases 


2-D 
Ridge 


2-D 
Escarp. 


3-D 

Axisym. 
Hill 


0.20 


0.29 


0.17 


0.21 


0.00 


1.00 


1.00 


0.00 


1.00 


1.00 


1.00 


0.25 


0.36 


0.21 


0.26 


0.50 


0.88 


0.67 


0.10 


0.74 


0.78 


0.67 


0.30 


0.43 


0.26 


0.32 


1.00 


0.75 


0.33 


0.20 


0.55 


0.61 


0.45 


0.35 


0.51 


0.30 


0.37 


1.50 


0.63 


0.00 


0.30 


0.41 


0.47 


0.30 


0.40 


0.58 


0.34 


0.42 


2.00 


0.50 


0.00 


0.40 


0.30 


0.37 


0.20 


0.45 


0.65 


0.38 


0.47 


2.50 


0.38 


0.00 


0.50 


0.22 


0.29 


0.14 


0.50 


0.72 


0.43 


0.53 


3.00 


0.25 


0.00 


0.60 


0.17 


0.22 


0.09 










3.50 


0.13 


0.00 


0.70 


0.12 


0.17 


0.06 










4.00 


0.00 


0.00 


0.80 


0.09 


0.14 


0.04 
















0.90 


0.07 


0.11 


0.03 
















1.00 


0.05 


0.08 


0.02 
















1.50 


0.01 


0.02 


0.00 
















2.00 


0.00 


0.00 


0.00 



Notes: 

1 . For values of H/L h? x/L h and z/L h other than those shown, linear interpolation is permitted. 

2. For H/L h > 0.5, assume H/L h = 0.5 for evaluating K] and substitute 2H for L h for evaluating K 2 and K 3 . 

3. Multipliers are based on the assumption that wind approaches the hill or escarpment along the direction 
of maximum slope. 

4. Notation: 

H: Height of hill or escarpment relative to the upwind terrain, in feet (meters). 

L h : Distance upwind of crest to where the difference in ground elevation is half the height of 

hill or escarpment, in feet (meters). 
Kf. Factor to account for shape of topographic feature and maximum speed-up effect 

K 2 : Factor to account for reduction in speed-up with distance upwind or downwind of crest. 

K 3 : Factor to account for reduction in speed-up with height above local terrain, 

x: Distance (upwind or downwind) from the crest to the building site, in feet (meters). 

z: Height above local ground level, in feet (meters), 

p.: Horizontal attenuation factor. 

y: Height attenuation factor. 



Minimum Design Loads for Buildings and Other Structures 



47 



Topographic Factor, K zt ~ Method 2 



Figure 6-4 (cont'd) f 



Equations : 

K zt =(l + K I K 2 K 3 ) 2 

Kj determined from table below 



K 2 =(l- J r i -) 



K- 



_ P -7z/Lh 



Parameters for Speed-Up Over Hills and Escarpments 


Mill Shape 


K^tH/Lh) 


Y 


U 


Exposure 


Upwind 
of Crest 


Downwind 
of Crest 


B 


C 


D 


2-dimensional ridges 

(or valleys with negative 
HinK^H/Lh) 


1.30 


1.45 


1.55 


3 


1.5 


1.5 


2-dimensional escarpments 


0.75 


0.85 


0.95 


2.5 


1.5 


4 


3-dimensional axisym. hill 


0.95 


1.05 


1.15 


4 


1.5 


1.5 



48 



ASCE 7-02 



Main Wind Force Res, Sys. / Corap and Clad. - Method 2 



AH Heights 



Figure 6-5 



| Internal Pressure Coefficient, GC pS 



Enclosed, Partially Enclosed, and Open Buildings 



Wails & Roofs 



Enclosure Classification 


GC^ 


Open Buildings 


0.00 


Partially Enclosed Buildings 


+0.55 
-0.55 


Enclosed Buildings 


+0.18 

-0.18 



Notes: 

1 . Plus and minus signs signify pressures acting toward and away 
from the internal surfaces, respectively. 

2. Values of GC pi shall be used with q z or q h as specified in 6.5.12. 

3. Two cases shall be considered to determine the critical load 
requirements for the appropriate condition: 

(i) a positive value of GC pi applied to all internal surfaces 
(ii) a negative value of GC pi applied to all internal surfaces 



Minimum Design Loads for Buildings and Other Structures 



49 



Main Wind Force Resisting System - Method 2 



AM Heights 



Figure 6-6 f Exteniri Pressure Coefficients, C p 



Enclosed, Partially Enclosed Baiidings 



Walls & Roofs 



WIND 



U<x p 



—~ B 



-»ss — - — £ t»- 



'**«> 
«*«, 



"BT«, 




5 **«> 



PLAN 



ELEVATION 



GABLE, HIP ROOF 



■ ffTMily 



?*<*, 



»*<*, 




ELEVATION ELEVATION 

MONOSLOPEROOF (NOTE 4) 



WIND 



*,«> 



*— J? 



PP 



wmm 



«»«> 



=»*«i 



«*Sm 



MEU 



PLAN 



«* 


&#2» 


Jmp 


| 


1 


'-Ulltr 


©s- 

te» 

Bsp- 

@b» 

Ess, 


f*^ 










F ( 


^ ™ - x - 

ELEVATION 

NOTES) 









50 



ASCE 7-02 



Main Wind Force Resisting System - Method 2 



Figure 6-6 (con't) j Externa! Pressure Coefficients, C p 



Ail Heights 



Enclosed, Partially Enclosed Buildings 



Walls & Roofs 



Surface 



Windward Wall 



Leeward Wall 



Side Wall 



Wall Pressure Coefficients, C p 



L/B 



All values 



0-1 



>4 



All values 



0.8 



-0.5 



-0.3 



-0.2 



-0.7 



Use With 



qh 



qh 



Roof Pressure Coefficients, C p , for use with q h 



Wind 
Direction 



Windward 



Angle, 9 (degrees) 



h/L 



10 



15 



20 



25 



30 



35 



45 



>60# 



Leeward 



Angle, 8 (degrees) 



10 



15 >20 



Normal 

to 
ridge for 
0>10° 



<0.25 



-0.7 
-0.18 



-0.5 
0.0* 



-0.3 
0.2 



-0.2 
0.3 



-0.2 
0.3 



0.0* 
0.4 



0.4 



0.019 



-0.3 



-0.5 



-0.6 



0.5 



-0.9 
-0.18 



-0.7 
-0.18 



-0.4 
0.0* 



-0.3 
0.2 



-0.2 
0.2 



-0.2 
0.3 



0.0* 
0.4 



0.01 9 



-0.5 



-0.5 



-0.6 



>1.0 



-1 3** 
-0.18 



-1.0 
-0.18 



-0.7 
-0.18 



-0.5 
0.0* 



-0.3 
0.2 



-0.2 
0.2 



0.0* 
0.3 



0.019 



-0.7 



-0.6 



-0.6 



Normal 

to 

ridge for 

9<10 

and 
Parallel 
to ridge 

for all 8 



Horiz distance from 

windward edge 



to h/2 



<0.5 



h/2 to h 



h to 2 h 



>2h 



> 1.0 



to h/2 



>h/2 



-0.9,-0.18 



-0.9,-0.18 



-0.5 9 -0.18 



-0.3,-0.18 



-1.3**, 
0.18 



-0.7,-0.18 



* Value is provided for interpolation 
purposes. 

** Value can be reduced linearly with area 
over which it is applicable as follows 



Area (sq ft) 



<100(9.3sqm) 



200 (23.2 sqm) 



> 1000 (92.9 sq m) 



Reduction Factor 



1.0 



0.9 



0.8 



Notes: 

1 . Plus and minus signs signify pressures acting toward and away from the surfaces, respectively. 

2. Linear interpolation is permitted for values of L/B, h/L and 9 other than shown. Interpolation shall only be 
carried out between values of the same sign. Where no value of the same sign is given, assume 0.0 for 
interpolation purposes. 

3. Where two values of C p are listed, this indicates that the windward roof slope is subjected to either 
positive or negative pressures and the roof structure shall be designed for both conditions. Interpolation 
for intermediate ratios of h/L in this case shall only be carried out between C p values of like sign. 

4. For monoslope roofs, entire roof surface is either a windward or leeward surface. 

5. For flexible buildings use appropriate Gy-as determined by Section 6.5.8. 

6. Refer to Figure 6-7 for domes and Figure 6-8 for arched roofs. 

7. Notation: 

B: Horizontal dimension of building, in feet (meter), measured normal to wind direction. 

L: Horizontal dimension of building, in feet (meter), measured parallel to wind direction. 

h: Mean roof height in feet (meters), except that eave height shall be used for 9 < 10 degrees. 

z: Height above ground, in feet (meters). 

G: Gust effect factor. 

q z ,qh' Velocity pressure, in pounds per square foot (N/m 2 ), evaluated at respective height. 

9: Angle of plane of roof from horizontal, in degrees. 

8. For mansard roofs, the top horizontal surface and leeward inclined surface shall be treated as leeward 
surfaces from the table. 

9. Except for MWFRS's at the roof consisting of moment resisting frames, the total horizontal shear shall not 
be less than that determined by neglecting wind forces on roof surfaces. 

#For roof slopes greater than 80°, use C p = 0.8 



Minimum Design Loads for Buildings and Other Structures 



51 



Main Wind Force Resisting System - Method 2 



1 External Pressure Coefficients, C» 



All Heights 



Figure 6-7 



Enclosed, Partially Enclosed Buildings and Structures 



Domed Roofs 



Wind 




A(h D /D = 0) 



A(h D /D = 0.25) 




C(h D /D>0.5) 



Notes: 



B(h D /D = 0) 
B(h D /D>0.5) 



0.1 0.2 0.3 0.4 

Ratio of Rise to Diameter, f/D 

External Pressure Coefficients for Domes with a Circular Base* 
(Adapted from Eurocode, 1995) 



1 . Two load cases shall be considered: 

Case A. C p values between A and B and between B and C shall be determined by linear 
interpolation along arcs on the dome parallel to the wind direction; 

Case B. C p shall be the constant value of A for < 25 degrees, and shall be determined by linear 
interpolation from 25 degrees to B and from B to C. 

2. Values denote C p to be used with q ( hn+f) where h D + f is the height at the top of the dome. 

3. Plus and minus signs signify pressures acting toward and away from the surfaces, respectively. 

4. C p is constant on the dome surface for arcs of circles perpendicular to the wind direction; for example, 
the arc passing through B-B-B and all arcs parallel to B-B-B. 

5. For values of h D /D between those listed on the graph curves, linear interpolation shall be permitted. 

6. 6-0 degrees on dome springline, 8-90 degrees at dome center top point, f is measured from 
springline to top. 

7. The total horizontal shear shall not be less than that determined by neglecting wind forces on roof 
surfaces. 

8. For f/D values less than 0.05, use Figure 6-6. 



52 



ASCE 7-02 



Main Wind Force Res. Sys. / Comp and Clad. - Method 2 



Figure 6-8 | External Pressure Coefficients, C, 



AH Heights 



L 



Enclosed, Partially Enclosed Buildings and Structures 



Arched Roofs 



Conditions 


Rise-to-span 
ratio, r 


c p 


Windward 
quarter 


Center 
half 


Leeward 
quarter 


Roof on elevated structure 


0<r<0.2 


-0.9 


-0.7 - r 


-0.5 


0.2<r<0.3* 


1.5r-0.3 


-0.7 - r 


-0.5 


0.3<r<0.6 


2.75r-0.7 


-0.7 - r 


-0.5 


Roof springing from ground level 


0<r<0.6 


\Ar 


-0.7 - r 


-0.5 



*When the rise-to-span ratio is 0.2 < r < 0.3, alternate coefficients given by 6r - 2.1 shall also be used for 
the windward quarter. 

Notes: 

1. Values listed are for the determination of average loads on main wind force resisting systems. 

2. Plus and minus signs signify pressures acting toward and away from the surfaces, respectively. 

3. For wind directed parallel to the axis of the arch, use pressure coefficients from Fig. 6-6 with wind 
directed parallel to ridge. 

4. For components and cladding: (1) At roof perimeter, use the external pressure coefficients in Fig. 6-1 1 
with 9 based on spring- line slope and (2) for remaining roof areas, use external pressure coefficients of 
this table multiplied by 0.87. 



Minimum Design Loads for Buildings and Other Structures 



53 



Main Wind Force Resisting System- Method 2 



All Heights 



Figure 6-9 



Design Wind Load Cases 



"wx 



?LX 

CASE 1 



t I t 



t t t T t t J 



*WY 



0. 75 P jyy 



Q.7SP 



wx 



*LY 



' 


' \ V V V V \ 


' 








■ 


' if v V ? V I 


I 



~-0.7SPix 






























,r V !f f V v ' 



0.7SPWX 



0.7SPJJZ 



By 



H- 



M r 



" f f t f t , f 



0,563 P wj 



0.75PWY 



0.75PLY 



0.563 PWX 



0-75P Ly 

CASE 3 

By 



rm 






T T T T T 0,563 Pry 

" f ? f T T ? 



0.563 P 



LY 



M T = 0. 75 (P W x+PLx)B x e x M T = 0. 75 (PwY+PiY)B Y e Y M T = 0.565 (Pwx+PLx)B x e x + ft J&? (PwY+Pu)B Y e Y 
e x = ±0.15B x e Y = ±0J5B Y e x = ±0J5B x e Y = ±0.15B Y 



CASE 2 



CASE 4 



Case 1 . Full design wind pressure acting on the projected area perpendicular to each principal axis of the 
structure, considered separately along each principal axis. 

Case 2. Three quarters of the design wind pressure acting on the projected area perpendicular to each 

principal axis of the structure in conjunction with a torsional moment as shown, considered separately 
for each principal axis. 

Case 3. Wind loading as defined in Case 1, but considered to act simultaneously at 75% of the specified 
value. 

Case 4. Wind loading as defined in Case 2, but considered to act simultaneously at 75% of the specified 
value. 

Notes: 

1. Design wind pressures for windward and leeward faces shall be determined in accordance with the 
provisions of 6.5.12.2.1 and 6.5.12.2.3 as applicable for building of all heights. 

2. Diagrams show plan views of building. 

3 . Notation: 

P\vx> Pfvy- Windward face design pressure acting in the x, y principal axis, respectively. 
Plx> Ply '* Leeward face design pressure acting in the x, y principal axis, respectively. 
£ fer- e Y ) ' Eccentricity for the x, y principal axis of the structure, respectively. 
M T : Torsional moment per unit height acting about a vertical axis of the building. 



54 



ASCE 7-02 



Main Wind Force Resisting System -Method 2 



h < 60 ft. 



Figure 6-10 g External Pressure Coefficients, GC p f 



Enclosed, Partially Enclosed Buildings 



Low-rise Walls & Roofs 






Transverse Direction 



Zone 2/3 Boundary 




Lonqitudinal Direction 

Basic Load Cases 



Minimum Design Loads for Buildings and Other Structures 



55 



Main Wind Force Resisting System - Method 2 



h < 60 ft. 



Figure 6-10 (cont'd) 



External Pressure Coefficients, GC p f 



Low-rise Walls & Roofs 



Enclosed, Partially Enclosed Buildings 



Roof 
Angle 8 

(degrees) 


Building Surface 


1 


2 


3 


4 


5 


6 


IE 


2E 


3E 


4E 


0-5 


0.40 


-0.69 


-0.37 


-0.29 


-0.45 


-0.45 


0.61 


-1.07 


-0.53 


-0.43 


20 


0.53 


-0.69 


-0.48 


-0.43 


-0.45 


-0.45 


0.80 


-1.07 


-0.69 


-0.64 


30-45 


0.56 


0.21 


-0.43 


-0.37 


-0.45 


-0.45 


0.69 


0.27 


-0.53 


-0.48 


90 


0.56 


0.56 


-0.37 


-0.37 


-0.45 


-0.45 


0.69 


0.69 


-0.48 


-0.48 



Notes: 

1 . Plus and minus signs signify pressures acting toward and away from the surfaces, respectively. 

2. For values of 6 other than those shown, linear interpolation is permitted. 

3. The building must be designed for all wind directions using the 8 loading patterns shown. The 
load patterns are applied to each building corner in turn as the Reference Corner. 

4. Combinations of external and internal pressures (see Figure 6-5) shall be evaluated as required to 
obtain the most severe loadings. 

5. For the torsional load cases shown below, the pressures in zones designated with a "T" (IT, 2T ; 
3T, 4T) shall be 25% of the full design wind pressures (zones 1, 3, 3, 4). 

Exception: One story buildings with h less than or equal to 30 fit (9.1m), buildings two stories 
or less framed with light frame construction, and buildings two stories or less designed with 
flexible diaphragms need not be designed for the torsional load cases. 

Torsional loading shall apply to all eight basic load patterns using the figures below applied at each 

reference corner. 

6. Except for moment-resisting frames, the total horizontal shear shall not be less than that 
determined by neglecting wind forces on roof surfaces. 

For the design of the MWFRS providing lateral resistance in a direction parallel to a ridge line or 
for flat roofs, use = 0° and locate the zone 2/3 boundary at the mid-length of the building. 
The roof pressure coefficient GC P /, when negative in Zone 2, shall be applied in Zone 2 for a 
distance from the edge of roof equal to 0.5 times the horizontal dimension of the building parallel 
to the direction of the MWFRS being designed or 2.5/z, whichever is less; the remainder of Zone 2 
extending to the ridge line shall use the pressure coefficient GC P / for Zone 3. 
Notation: 
a: 10 percent of least horizontal dimension or 0.4h, whichever is smaller, but not less than either 

4% of least horizontal dimension or 3 ft (0.9 m). 
h: Mean roof height, in feet (meters), except that eave height shall be used for < 10°. 
0: Angle of plane of roof from horizontal, in degrees. 



7 





Transverse Direction Longitudinal Direction 

Torsional Load Cases 



56 



ASCE 7-02 



§lii$j!$!^^ 



Figure 6-11 A 



h < 60 ft 



i External Pressure Coefficients, GC p 



Enclosed, Partially Enclosed Buildings 



Walls 




o 
o 



"o 

a 
O 

g> 

CO 

CO 

01 
&» 

Q. 

15 

c 
&„. 

3 



Notes: 



10 



500 



-1.8 
-1.6 
-1.4 
-1.2 

-1.0 

-0.8 
-0.6 
-0.4 
-0.2 



+0.2 
+0.4 
+0.6 
+0.8 

+1.0 

+1.2 

















&> 


n^^ 












r^ 








vv ■ ■ 
















































































































































®&l5j 





























-1.4 
-1.1 
-0.8 



+0.7 
+1.0 



1 10 20 50 100 200 5001000 

(0.1) (0.9) (1.9) (4.6) (9.3) (18.6) (46.5) (92.9) 

Effective Wind Area, ft 2 (irf) 



1 . Vertical scale denotes GC P to be used with q h . 

2. Horizontal scale denotes effective wind area, in square feet (square meters). 

3. Plus and minus signs signify pressures acting toward and away from the surfaces, respectively 

4. Each component shall be designed for maximum positive and negative pressures. 

5. Values of GC p for walls shall be reduced by 10% when G < 10°. 

6. Notation: 

a: 10 percent of least horizontal dimension or 0.4h, whichever is smaller, but not less than either 4% 

of least horizontal dimension or 3 ft (0.9 m). 
h: Mean roof height, in feet (meters), except that eave height shall be used for < 10°. 
B: Angle of plane of roof from horizontal, in degrees. 



Minimum Design Loads for Buildings and Other Structures 



57 



Components and Cladding - Method 2 



Figure 6-1 1 B | External Pressure Coefficients, GC p 



h < 60 ft 



Enclosed, Partially Enclosed Buildings 



Gable Roofs 9 < 7 C 



© 


© 


© 


© 


© 


© 


© 


© 


© 


© 


© 


© 




-3.2 
-3.0 

-2.8 
-2.6 
-2.4 

-2 -2.0 

£ -1.8 



10 



100 



o 

CD 



© 

O 



m 
m 

m 



-1.6 
-1.4 
-1.2 

-1.0 

-0.8 
-0.6 



■= -0-4 



a. 



E -°- 2 
£ 

£ +0-2 
+0.4 
+0.6 









i 






~© 






Roof 








V 














\ 














X 


i 














\ 










© 




\ 












X 


v \ 














V 


\ 












x 


^ 








© 




















































































-GX?)*®- 


















********* 

























o 

CD 



10 



100 



-3.2 



-2.8 



-1.8 



-1.1 
-1.0 
-0.9 



+0.2 
+0.3 



«j -3.0 

-2.8 
-2.6 
-2.4 
-2.2 

-2.0 
-1.8 
-1.6 
-1.4 
-1.2 

-1.0 
-0.8 



-0.6 



"o 

& 
o 
O 
m 

3 

m 

m 

m 










I I 






-® 




Overhana 








V 














\ 














\ 
















V 










^D*© — 




V 














^ 
















V 














\ 














\ 























-2.8 



-1.7 
-1.6 



-1.1 



-0.8 



1 10 20 50 100 200 5001000 

(0.1) (0.9) (1.9) (4.6) (9.3) (18.6) (46.5) (92.9) 

Effective Wind Arw, ft 2 (rf) 



1 10 20 50 100 200 5001000 

(0.1) (0.9) (1.9) (4.6) (9.3) (18.6) (46.5) (92.9) 

Effective Wind Area, ft 2 (d ) 



Notes: 

1 . Vertical scale denotes GC P to be used with q h . 

2. Horizontal scale denotes effective wind area, in square feet (square meters). 

3. Plus and minus signs signify pressures acting toward and away from the surfaces, respectively. 

4. Each component shall be designed for maximum positive and negative pressures. 

5. If a parapet equal to or higher than 3 ft (0.9m) is provided around the perimeter of the roof with < 7°, 
Zone 3 shall be treated as Zone 2. 

6. Values of GC P for roof overhangs include pressure contributions from both upper and lower surfaces. 

7. Notation: 

a: 1 percent of least horizontal dimension or 0.4h, whichever is smaller, but not less than either 4% of 

least horizontal dimension or 3 ft (0.9 m). 
h: Eave height shall be used for < 10°. 
8: Angle of plane of roof from horizontal, in degrees. 



58 



ASCE 7-02 



il;^^ 



Figure 6-1 1 C j External Pressure Coefficients, G€ p 



h<60ft. 



Enclosed, Partially Enclosed Buildings 



Gable/Hip Roofs 7°< 8 < IT 



a \,a\ 



® 



® 



® 



© 



©: © :© 



© 



® 



®! 



® 



© 



© © 



© 



® 



© 




* 



(3) 


® / > 


GJ 


® 


a \ , \ a 


/ 
® 







© 


(T) 




O 
CD 

"o 

O 
O 



Z3 



CO 

E 



-2.8 
-2.6 
-2.4 
-2.2 
-2.0 
-1.8 
-1.6 
-1.4 
-1.2 

-1.0 

-0.8 
-0.6 
-0.4 
-0.2 



+0.2 
+0.4 
+0.6 
+0.8 



10 




100 




















_^ 
























Roof 














































® 




























<T> 














\JJ 




















































































^X5X3>- 





























-2.6 



-2.0 
-1.7 



-1.2 



-0.9 
-0.8 



+0.3 
+0.5 



1 10 20 50 100 200 5001000 

(0.1) (0.9) (1.9) (4.6) (9.3) (18.6) (46.5) (92.9) 

Effective Wind Area, ft 2 (m 2 ) 



o 



"o 

o 
O 

</> 
w 

CD 



3 
LU 



4.0 

-3.8 


10 




100 






^ 














viy 


V 






Overhana 


-3.6 
-3.4 






\ 














^ 


V 










-i.i 

•3.0 






\ 














A 


^ 
















\ 








-£.v 
























'LA 


(2) 































-3.7 



-2.5 



-2.2 



1 10 20 50 100 200 5001000 
(0.1) (0.9) (1.9) (4.6) (9.3) (18.6) (46.5) (92.9) 

Effective Wind Area, ft 2 (m 2 ) 



Notes: 

1 . Vertical scale denotes GC P to be used with q h . 

2. Horizontal scale denotes effective wind area, in square feet (square meters). 

3. Plus and minus signs signify pressures acting toward and away from the surfaces, respectively. 

4. Each component shall be designed for maximum positive and negative pressures. 

5 . Values of GC P for roof overhangs include pressure contributions from both upper and lower surfaces. 

6. For hip roofs with 7° < < 27°, edge/ridge strips and pressure coefficients for ridges of gabled roofs shall 
apply on each hip. 

7. For hip roofs with 9 < 25°, Zone 3 shall be treated as Zone 2. 

8. Notation: 

a: 1 percent of least horizontal dimension or 0.4h, whichever is smaller, but not less than either 4% of 

least horizontal dimension or 3 ft (0.9 m). 
h: Mean roof height, in feet (meters), except that eave height shall be used for 8 < 1 0°. 
0: Angle of plane of roof from horizontal, in degrees. 



Minimum Design Loads for Buildings and Other Structures 



59 



Components and Cladding- Method 2 



Figure 6-1 ID j External Pressure Coefficients GC p 



h < 60 ft. 



Enclosed, Partially Enclosed Buildings 



Gable Roofs 27°< 9 < 45° 



a\,a 



®j ® j®® L ® m 



®: 



® 



®® ® 



:® 



w. ® i<afer ® r® 



cl 




O 
O 


-1.6 


^* 


-1.4 




-1.2 


o 


-1.0 


«£: 


-08 


<oo 




o 


-0.6 


o 


-04 


m 




3 


-0.2 


CO 
CO 





8 


+0.2 


£L 


+0.4 


CO 

C 


+0.6 




+0.8 


X +1.0 


LU 





10 



100 

















®&® 






Roof 




















® 
















































































































-<M)*(D- 



























•1.2 
-1.0 
-0.8 



+0.8 
+0.9 



1 10 20 50 100 200 5001000 

(0.1) (0.9) (1.9) (4.6) (9.3) (18.6) (46.5) (92.9) 

Effective Wind Area, ft 2 (nf) 




a. 
O 



■3.0 



10 



100 



**• -2.8 



C 

1 

© 

O 

£ 

CO 
CO 



-2.6 
-2.4 
-2.2 
-2.0 
-1.8 
-1.6 
■1.4 
-1.2 



= -1.0 





















Overhang 


































&>*ci> 





















































































-2.0 
-1.8 



yj 



1 10 20 50 100 200 5001000 
(0.1) (0.9) (1.9) (4.6) (9.3) (18.6) (46.5) (92.9) 

Effective Wind Area, ft 2 (nr^ ) 



Notes: 

1 . Vertical scale denotes GC P to be used with q h . 

2. Horizontal scale denotes effective wind area, in square feet (square meters). 

3. Plus and minus signs signify pressures acting toward and away from the surfaces, respectively. 

4. Each component shall be designed for maximum positive and negative pressures. 

5. Values of GC P for roof overhangs include pressure contributions from both upper and lower surfaces. 

6. Notation: 

a: 10 percent of least horizontal dimension or 0.4h, whichever is smaller, but not less than either 4% of 

least horizontal dimension or 3 ft (0.9 m). 
h: Mean roof height, in feet (meters). 
6: Angle of plane of roof from horizontal, in degrees. 



60 



ASCE 7-02 



Components and Cladding - Method 2 



Figure 6-12 | External Pressure Coeffici ents, GCp 

Enclosed, Partially Enclosed Buildings 



h < 60 ft. 



Stepped Roofs 





Notes: 



A, £10 ft. (3 m) 
* = 1.5h 1 

b < 100 ft. (30.5 m) 

^- = 0.3 to 0.7 
h 

W. 

— =- = 0.25 to 0.75 
W 



On the lower level of flat, stepped roofs shown in Fig. 6-12, the zone designations and pressure 

coefficients shown in Fig. 6-1 IB shall apply, except that at the roof-upper wall intersection(s), Zone 

3 shall be treated as Zone 2 and Zone 2 shall be treated as Zone 1 . Positive values of GC P equal to 

those for walls in Fig. 6-1 1 A shall apply on the cross-hatched areas shown in Fig. 6-12. 

Notation: 

b: 1 .S/i! in Fig. 6-12, but not greater than 1 00 ft (30.5 m). 

h: Mean roof height, in feet (meters). 

h,\ h } or /* 2 in Fig. 6-\2;h = h ] + h 2 ;h x > 10 ft (3.1 m); h { /h = 0.3 to 0.7. 

W: Building width in Fig. 6-12. 

W { : W x or W 2 or W 2 in Fig. 6-12. W=W 1 + W 2 oyWi + W 2 + W^ W-JW~ 0.25 to 0.75. 

8: Angle of plane of roof from horizontal, in degrees. 



Minimum Design toads for Buildings and Other Structures 



61 



Components anti >^^i^^:!!S|^|^-^ 



Figure 6-13 



h < 60 ft. 



1 Externa! Pressure Coefficients, GC™ 



Enclosed, Partially Enclosed Buildings 



Multispae Gable Roofs 






"o 

fa 
a* 
© 
O 



0> 






-ft' 



M7®. 




ELEVATION OF BUILDING 
(2 or More Spans) 



■t - - 



®i 



® 



r@t ® 



sos^a 



®® © 



i® 



m® ® i®i 




r 



PLAN AND ELEVATION OF 
A SINGLE SPAN WIOOULE 



-3.0 

-2.8 
-2.6 
-2.4 



10 



100 



f£ -2.2 



-2.0 

-1.8 
-1.6 
-1.4 
-1.2 
-1.0 
-0.8 
-0.6 



-= -0-4 
^ -0.2 

s o 

+0.4 
+0.6 
+0.8 



(^ 






i i 




\2J 


V 




10° < 8*30° 








\ 












~® — 




\ 












"X 


A 










TD ■ — 




> 


N 








W 












































































































































"-(iXD&iir 





























-2.7 

-2.2 

-1.7 
-1.6 
-1.4 



+0.4 
+0.6 



O 



o 

o 
£ 

CO 

CO 

fi 

a, 
TB 

I 



1 10 20 50 100 200 5001000 

(0.1) (0.9) (1.9) (4.6) (9.3) (18.6) (46.5) (92.9) 

Effective Wind Area, ft 2 (rf) 



-3.0 

-2.8 
-2.6 


10 




100 












| 




(1) 






30°^e^4i° 






^ 












-2.4 
-2.2 
-2.0 

-1.8 


l^\ 


© 


^ 


k. 














X 










CD 


\ 


^ 


V 










■^ 


k 


^% 








-1.6 
-1.4 
-1.2 












\ 














^ 


\j 






















-1.0 

-0.8 
-0.6 
-0.4 
-0.2 

+0.2 
+0.4 
+0.6 
+0.8 
+1.0 

jM 






































































































































"®®*ST 





























-2.6 
-2.5 

-2.0 
-1.7 



-1.1 



+0.8 
+1.0 



1 10 20 50 100 200 5001000 

(0.1) (0.9) (1.9) (4.6) (9.3) (18.6) (46.5) (92.9) 

Effective Wind Area, ft 2 (d) 



Notes: 

1 . Vertical scale denotes GC P to be used with q^. 

2. Horizontal scale denotes effective wind area A, in square feet (square meters). 

3. Plus and minus signs signify pressures acting toward and away from the surfaces, respectively. 

4. Each component shall be designed for maximum positive and negative pressures. 

5 . For 6 < 1 0°, values of GC P from Fig. 6- 1 1 shall be used. 

6. Notation: 
10 percent of least horizontal dimension of a single-span module or OAh, whichever is 
smaller, but not less than either 4 percent of least horizontal dimension of a single-span 
module or 3 ft (0.9 m). 

Mean roof height, in feet (meters), except that eave height shall be used for < 10°. 
Building module width, in feet (meters). 
Angle of plane of roof from horizontal, in degrees. 



a: 



h: 

W\ 
0: 



62 



ASCE 7-02 



:$|p$!i^^ 



Figure 6-14A | External Pressure Coefficients, GC p 



h <, 60 ft. 



Enclosed, Partially Enclosed Buildings 



Monoslope Roofs 

3°< e < io° 



2a 



2a 



4 



4 



© 



© 



® 



I 



© \® 






® 



fe 



_ L_ 



© :® 



a 







Q 
O 

c 
m 

o 

•C 
o> 

o 

o 

3 
£0 
CO 

lb. 

a, 

"5 

c 

X 
UJ 



-3.0 

-2.8 
-2.6 
-2.4 
■2.2 

-2.0 

-1.8 
-1.6 
-1.4 
-1.2 

-1.0 
-0.8 
-0.6 
-0.4 
-0.2 

+0.2 
+0.4 
+0.6 



10 




100 




















(£) 
















V 














\ 


v 














\ 










(1) 




\: 


k^ 








It) 




^ 


\ 








(?) 














v*y 




























/T\ 














CD 






































































ALL ZONES 











































-2.6 



-1.8 

-1.6 
-1.5 

-1.3 
-1.2 
-1.1 



+0.2 
+0.3 



1 

(0.1) 



10 20 50 100 200 5001000 

(0.9) (1.9) (4.6) (9.3) (18.6) (46.5) (92.9) 



Effective Wind Area, ft 2 (m 2 ) 



Notes: 

1 . Vertical scale denotes GC P to be used with q h . 

2. Horizontal scale denotes effective wind area A, in square feet (square meters). 

3. Plus and minus signs signify pressures acting toward and away from the surfaces, respectively. 

4. Each component shall be designed for maximum positive and negative pressures. 

5. For 9 < 3°, values of GC P from Fig. 6-1 IB shall be used. 

6. Notation: 

a: 1 percent of least horizontal dimension or 0.4/*, whichever is smaller, but not less than 

either 4 percent of least horizontal dimension or 3 ft (0.9 m). 
h: Eave height shall be used for 9 < 10°. 
W\ Building width, in feet (meters). 
6: Angle of plane of roof from horizontal, in degrees. 



Minimum Design Loads for Buildings and Other Structures 



63 



Components and Clad cling- >lethod 2 



Figure 6-1 4B [ External Pressure Coefficients, GC p 



h 5 60 ft. 



Enclosed, Partially Enclosed Buildings 



Monoslope Roofs 
10°<8<30° 



2a 



4 



4 



® 



® 



© 



TS" 



® © 



& 




w 



Q. 
O 
(D 

c 
o 

15 
o 
o 

£ 

m 
a, 

15 

c 
h,* 

m 

x 

yj 



-3.0 

■2.8 
-2.6 
■2.4 
-2.2 

-2.0 

-1.8 
■1.6 
■1.4 
-1.2 

-1.0 
-0.8 
-0.6 
-0.4 
-0.2 

+0.2 
+0.4 
+0.6 



10 



100 





V 












fi\ 


(A) 


\ 


ht 














\ 














\ 


s. 














\ 






















& 










































(D 








































































































ALL ZONES 





























-2.9 



-2.0 



■1.6 

-1.3 
-1.2 
-1.1 



+0.3 
+0.4 



1 
(0.1) 



10 20 50 100 200 5001000 

(0.9) (1.9) (4.6) (9.3) (18.6) (46.5) (92.9) 



Effective Wind Area, ft 2 (m 2 ) 



Notes: 

1 . Vertical scale denotes GC P to be used with g h . 

2. Horizontal scale denotes effective wind area A, in square feet (square meters). 

3. Plus and minus signs signify pressures acting toward and away from the surfaces, respectively. 

4. Each component shall be designed for maximum positive and negative pressures. 

5. Notation: 

a: 1 percent of least horizontal dimension or 0Ah> whichever is smaller, but not less than 

either 4 percent of least horizontal dimension or 3 ft (0.9 m). 
h: Mean roof height, in feet (meters). 
W\ Building width, in feet (meters). 
9: Angle of plane of roof from horizontal, in degrees. 



64 



ASCE 7-02 



flllBi^ 



Figure 6-15 | External Pressure Coefficients, GC p 



h < 60 ft 



Enclosed, Partially Enclosed Buildings 



Sawtooth Roofs 



€N$ 



<3 



®r-- 


__(£)____ 


^ 


- "1 






3) 


® 


® 


_ J 




S 


[3Jr 


© 




w 



Elevation of Building 
(2 or More Spans) 



Notes: 



10 



100 



500 



O 



m 
'5 



-4.4 
-4.2 

-4.0 

-3.8 
-3.6 
-3.4 
-3.2 

-3.0 

-2.8 
-2.6 
-2.4 



HT -2.2 



m 
o 

O 

E 

3 

m 
m 
m 



-2.0 

-1.8 
-1.6 
-1.4 
-1.2 

-1.0 



m -0.8 



£ -0.6 



m 
yj 



-0.4 




-0.2 



+0.2 
+0.4 
+0.6 
+0.8 
+1.0 
+1.2 
+1.4 



f^(SPANA) 














v2/ 


**H 




















































(2) 










































(|)(SPANSB,C* 


D) 




















V 


~A 




& 








v 


s. \ 














V 














v \ 






























































































































































(T* 












v -i-' 














(3^ 




























^ 


^J 















-4.1 



-3.7 



-3.2 



-2.6 



-2.2 
-2.1 

-1.9 
-1.6 



-1.1 



+0.4 

+0.7 
+0.8 

+1.1 



1 

(0-1) 



10 20 
(0.9) (1.9) 



50 100 200 

(4.6) (9.3) (18.6) 



5001000 

(46.5) (92.9) 



Effective Wind Area, ft 2 (m 2 ) 



1 . Vertical scale denotes GC P to be used with q h . 

2. Horizontal scale denotes effective wind area A, in square feet (square meters). 

3. Plus and minus signs signify pressures acting toward and away from the surfaces, respectively. 

4. Each component shall be designed for maximum positive and negative pressures. 

5. For < 10°, values of GC P from Fig. 6-1 1 shall be used. 

6. Notation: 

a: 1 percent of least horizontal dimension or 0.4/?, whichever is smaller, but not less than either 4 

percent of least horizontal dimension or 3 ft (0.9 m). 
h: Mean roof height, in feet (meters), except that eave height shall be used for 6 < 1 0°. 
W\ Building width, in feet (meters). 
0: Angle of plane of roof from horizontal, in degrees. 



Minimum Design Loads for BuiBdings and Other Structures 



65 



|{toJii:jpri^^ 



Figure 6-16 



A!! Heights 



| External Pressure Coefficients, GCp 



Enclosed, Partially Enclosed Buildings and Structures 



Domed Roofs 



Wind 




f 
~J" Wind, 

n D 




D 



External Pressure Coefficients for Domes with a Circular Base 


0, degrees 


Negative 
Pressures 


Positive 
Pressures 


Positive 
Pressures 


0-90 


0-60 


61-90 


GC P 


-0.9 


+0.9 


+0.5 



Notes: 

1 . Values denote GC P to be used with q^+o where h D + f is the height at the top of the dome. 

2. Plus and minus signs signify pressures acting toward and away from the surfaces, respectively. 

3. Each component shall be designed for the maximum positive and negative pressures. 

4. Values apply to < h /D < 0.5, 0.2 < f/D < 0.5. 

5. = degrees on dome springline, 8 = 90 degrees at dome center top point, f is measured from 
springline to top. 



66 



ASCE 7-02 



:^l^iS^^§^§^^S^KM^^^^^S& 



Figure 6-17 j External Pressure Coefficients, GCp 



h > 60 ft. 



Enclosed, Partially Enclosed Buildings 



Walls & Roofs 



2a 



®J __<£>_ 



®! 



2a 



_ ! ® 



® 



© 



(D" V "0)" T IS) 



5 



10 20 



500 



o 
o 



-3.6 
-3.4 
-3.2 

-3.0 

-2.8 
-2.6 
-2.4 



V u 



ROOF PLAN 

Hi i a 



® 



® 



-® 



CD 

o 
O 



-2.0 

■1.8 
■1.6 
-1.4 
-1.2 

-1.0 

-0.8 

-0.6 

•= -0.4 

-0.2 



m 
m 

i 



m 



s 

+0.2 
+0.4 
+0.6 
+0.8 

+1.0 










































































(^ 














J^Z^™^*™-,*™^ 




























&> 

























































-0 
















































































































<T>&<T> 












vV & V*y 















-3.2 



-2.3 



-1.8 
-1.6 
-1.4 



-1.0 
-0.9 
-0.7 



+0.6 
+0.9 



1 
(0.1) 



10 20 

(0.9) (1.9) 



50 100 200 

(4.6) (9.3) (18.6) 



5001000 

(46.5) (92.9) 



Effective Wind Area, ft 2 (m 2 ) 



WALL ELEVATION 



Notes: 



1 . Vertical scale denotes GC P to be used with appropriate q z or q h . 

2. Horizontal scale denotes effective wind area A, in square feet (square meters). 

3. Plus and minus signs signify pressures acting toward and away from the surfaces, respectively. 

4. Use q z with positive values of GC P and q h with negative values of GC p . 

5. Each component shall be designed for maximum positive and negative pressures. 

6. Coefficients are for roofs with angle < 10°. For other roof angles and geometry, use GC p values 
from Fig. 6-1 1 and attendant q h based on exposure defined in 6.5.6. 

7. If a parapet equal to or higher than 3 ft (0.9m) is provided around the perimeter of the roof with 9 < 
10°, Zone 3 shall be treated as Zone 2. 

8. Notation: 

a: 1 percent of least horizontal dimension, but not less than 3 ft (0.9 m). 

h: Mean roof height, in feet (meters), except that eave height shall be used for 8 < 1 0°. 

z: height above ground, in feet (meters). 

9: Angle of plane of roof from horizontal, in degrees. 



Minimum Design Loads for Buildings and Other Structures 



67 



Main Wind Force Resisting System - Method 2 



All Heights 



Figure 6-18 



I 



Force Coefficients, C f 



Open Buildings 



Moiioslope Roofs 



Roof angle 
degrees 


L/B 


5 


3 


2 


1 


1/2 


1/3 


1/5 


10 


0.2 


0.25 


0.3 


0.45 


0.55 


0.7 


0.75 


15 


0.35 


0.45 


0.5 


0.7 


0.85 


0.9 


0.85 


20 


0.5 


0.6 


0.75 


0.9 


1.0 


0.95 


0.9 


25 


0.7 


0.8 


0.95 


1.15 


1.1 


1.05 


0.95 


30 


0.9 


1.0 


1.2 


1.3 


1.2 


1.1 


1.0 



Roof angle 9 
degrees 


Center of Pressure X/L 


L/B 


2 to 5 


1 


1/5 to 1/2 


10 to 20 


0.35 


0.3 


0.3 


25 


0.35 


0.35 


0.4 


30 


0.35 


0.4 


0.45 



Notes 
1 



Wind forces act normal to the surface. Two cases shall be considered: (1) wind forces directed 
inward; and (2) wind forces directed outward. 

The roof angle shall be assumed to vary ± 10 D from the actual angle and the angle resulting in the 
greatest force coefficient shall be used. 

Notation: 

B: dimension of roof measured normal to wind direction, in feet (meters); 

L: Dimension of roof measured parallel to wind direction, in feet (meters); 

X: Distance to center of pressure from windward edge of roof, in feet (meters); and 

9: Angle of plane of roof from horizontal, in degrees. 



68 



ASCE 7-02 



Other Structures - Method 2 



AH Heights 



Figure 6-19 



Force Coefficients, C f 



Chimneys, Tanks, Rooftop 
Equipment, & Similar Structures 



Cross-Section 


Type of Surface 


h/D 


1 


7 


25 


Square (wind normal to face) 


All 


13 


1.4 


2.0 


Square (wind along diagonal) 


All 


1.0 


1.1 


1.5 


Hexagonal or octagonal 


All 


1.0 


1.2 


1.4 


Round (D^7>2e5) 

(D^g7 > 53, D in m, q z m N/m 2 ) 


Moderately smooth 


0.5 


0.6 


0.7 


Rough (DVD = 0.02) 


0.7 


0.8 


0.9 


Very rough (DVD = 0.08) 


0.8 


1.0 


1.2 


Round {D^q~ z <2S) 
{D^q~ z < 53, D in m, q z in N/m 2 ) 


All 


0.7 


0.8 


1.2 



Notes: 

1 . The design wind force shall be calculated based on the area of the structure projected on a plane normal 
to the wind direction. The force shall be assumed to act parallel to the wind direction. 

2. Linear interpolation is permitted for h/D values other than shown. 

3. Notation: 

D: diameter of circular cross-section and least horizontal dimension of square, hexagonal or octagonal 
cross-sections at elevation under consideration, in feet (meters); 

D': depth of protruding elements such as ribs and spoilers, in feet (meters); and 

h: height of structure, in feet (meters); and 

q z : velocity pressure evaluated at height z above ground, in pounds per square foot (N/m 2 ). 



Minimum Design Loads for Buildings and Other Structures 



Other Structures - Method 2 



AH Heights 



Figure 6-20 



Force Coefficients, C f 



Solid Freestanding 
Walls & Solid Signs 



At Ground Level 


Above Ground Level 


V 


9 


M/N 


9 


<3 


1.2 


<6 


1.2 


5 


1.3 


10 


1.3 


8 


1.4 


16 


1.4 


10 


1.5 


20 


1.5 


20 


1.75 


40 


1.75 


30 


1.85 


60 


1.85 


>40 


2.0 


>80 


2.0 



Notes: 

1 . The term "signs" in notes below applies also to "freestanding 
walls". 

2. Signs with openings comprising less than 30% of the gross area 
shall be considered as solid signs. 

3. Signs for which the distance from the ground to the bottom edge is 
less than 0.25 times the vertical dimension shall be considered to 
be at ground level. 

4. To allow for both normal and oblique wind directions, two cases 
shall be considered: 

a. resultant force acts normal to the face of the sign on a vertical 
line passing through the geometric center, and 

b. resultant force acts normal to the face of the sign at a distance 
from a vertical line passing through the geometric center equal 
to 0.2 times the average width of the sign. 

5. Notation: 

v: ratio of height to width; 

M: larger dimension of sign, in feet (meters); and 

N: smaller dimension of sign, in feet (meters). 



70 



ASCE 7-02 



Other Structures - Method 2 



All Heights 



Figure 6-21 



Force Coefficients, C f 



Open Signs & 
Lattice Frameworks 



e 


Flat-Sided 
Members 


Rounded Members 


(DVi7<5.3) 


Djf z >2.5 


<0.1 


2.0 


1.2 


0.8 


0.1 to 0.29 


1.8 


1.3 


0.9 


0.3 to 0.7 


1.6 


1.5 


1.1 



Notes: 

1 . Signs with openings comprising 30% or more of the gross area are 
classified as open signs. 

2. The calculation of the design wind forces shall be based on the area of 
all exposed members and elements projected on a plane normal to the 
wind direction. Forces shall be assumed to act parallel to the wind 
direction. 

3. The area A f consistent with these force coefficients is the solid area 
projected normal to the wind direction. 

4. Notation: 

g : ratio of solid area to gross area; 

D: diameter of a typical round member, in feet (meters); 

q z : velocity pressure evaluated at height z above ground in pounds per 
square foot (N/m 2 ). 



Minimum Design Loads for Buildings and Other Structures 



71 



Other Structures - Method 2 



All Heights 



Figure 6-22 



Force Coefficients, C f 



Open Structures 



Trussed Towers 



Tower Cross Section 


c r 


Square 


4.0 e 2 - 5.9 e +4.0 


Triangle 


3.4 e 2 - 4.7 e +3.4 



Notes: 

1 . For all wind directions considered, the area A/ consistent with the specified force 
coefficients shall be the solid area of a tower face projected on the plane of that 
face for the tower segment under consideration. 

2. The specified force coefficients are for towers with structural angles or similar flat- 
sided members. 

3. For towers containing rounded members, it is acceptable to multiply the specified 
force coefficients by the following factor when determining wind forces on such 
members: 

0.51 e 2 + 0.57, but not > 1.0 

4. Wind forces shall be applied in the directions resulting in maximum member forces 
and reactions. For towers with square cross-sections, wind forces shall be 
multiplied by the following factor when the wind is directed along a tower 
diagonal: 

1 +0.75 e, but not > 1.2 

5. Wind forces on tower appurtenances such as ladders, conduits, lights, elevators, 
etc., shall be calculated using appropriate force coefficients for these elements. 

6. Loads due to ice accretion as described in Section 1 1 shall be accounted for. 

7. Notation: 

e : ratio of solid area to gross area of one tower face for the segment under 
consideration. 



72 



ASCE 7-02 



Importance Factor, I (Wind Loads) 



Table 6-1 



Category 


Non-Hurricane Prone Regions 

and Hurricane Prone Regions 

with V- 85-100 mph 

and Alaska 


Hurricane Prone Regions 
with V > 100 mph 


I 


0.87 


0.77 


II 


1.00 


LOO 


III 


1.15 


1.15 


IV 


1.15 


1.15 



Note: 

1. The building and structure classification categories are listed in Table 1-1. 



Minimum Design Loads for Buildings and Other Structures 



73 



Terrain Exposure Constants 



Table 6-2 



Exposure 


a 


z g (ft) 


A 

a 


A 

b 


a 


b 


c 


um 


e 


Zmi„ (ft)* 


B 


7.0 


1200 


1/7 


0.84 


1/4.0 


0.45 


0.30 


320 


1/3.0 


30 


C 


9.5 


900 


1/9.5 


1.00 


1/6.5 


0.65 


0.20 


500 


1/5.0 


15 


D 


11.5 


700 


1/11.5 


L07 


1/9.0 


0.80 


0.15 


650 


1/8.0 


7 



^Zmin = minimum height used to ensure that the equivalent height z is greater of O.6/1 or 2^. 
For buildings with h < z^, z shall be taken as z^ n . 



74 



ASCE 7-02 



Velocity Pressure Exposure Coefficients, Kj, and K z J 






Table 6-3 [ 
















Height above 
ground level, z 


Exposure (Note 1) 




B 


C 


D 


ft 


(m) 


Case 1 


Case 2 


Cases 1 & 2 


Cases 1 & 2 


0-15 


(0-4.6) 


0.70 


0.57 


0.85 


1.03 


20 


(6.1) 


0.70 


0.62 


0.90 


1.08 


25 


(7.6) 


0.70 


0.66 


0,94 


1.12 


30 


(9.1) 


0.70 


0.70 


0.98 


1.16 


40 


(12.2) 


0.76 


0.76 


1.04 


1.22 


50 


(15.2) 


0.81 


0.81 


1.09 


1.27 


60 


(18) 


0.85 


0.85 


1.13 


1.31 


70 


(21.3) 


0.89 


0.89 


1.17 


1.34 


80 


(24.4) 


0.93 


0.93 


1.21 


1.38 


90 


(27.4) 


0,96 


0.96 


1.24 


1.40 


100 


(30.5) 


0.99 


0.99 


1.26 


1.43 


120 


(36.6) 


1.04 


1.04 


1.31 


1.48 


140 


(42.7) 


1.09 


1.09 


1.36 


1.52 


160 


(48.8) 


1.13 


1.13 


1.39 


1.55 


180 


(54.9) 


1.17 


1.17 


1.43 


1.58 


200 


(61.0) 


1.20 


1.20 


1.46 


1.61 


250 


(76.2) 


1.28 


1.28 


1.53 


1.68 


300 


(91.4) 


1.35 


1.35 


1.59 


1.73 


350 


(106.7) 


1.41 


1.41 


1.64 


1.78 


400 


(121.9) 


1.47 


1.47 


1.69 


1.82 


450 


(137.2) 


1.52 


1.52 


1.73 


1.86 


500 


(152.4) 


1.56 


1.56 


1.77 


1.89 


Notes: 

1. Case 1: a. All components and cladding. 

b. Main wind force resisting system in low-rise buildings designed using Figure 6-1C 

Case 2: a. All main wind force resisting systems in buildings except those in low-rise buildin 
designed using Figure 6- 1 0. 
b. All main wind force resisting systems in other structures. 

2. The velocity pressure exposure coefficient K z may be determined from the following formula: 

For 15 ft. <z< 2g Forz<15ft. 
K 2 = 2 .0 1 (z/z g ) 2/a K z - 2.0 1 ( 1 5/z g ) 2/a 
Note; z shall not be taken less than 30 feet for Case 1 in exposure B. 

3 . a and z g are tabulated in Table 6-2. 

4. Linear interpolation for intermediate values of height z is acceptable. 

5. Exposure categories are defined in 6.5.6. 





Minimum Design Loads for Buildings and Other Structures 



75 



Wind Directionality Factor, K^ 

Z2 



Table 6-4 



Structure Type 


Directionality Factor K#* 


Buildings 

Main Wind Force Resisting System 
Components and Cladding 


0.85 
0.85 


Arched Roofs 


0.85 


Chimneys, Tanks, and Similar Structures 
Square 
Hexagonal 

Round 


0.90 
0.95 
0.95 


Solid Signs 


0.85 


Open Signs and Lattice Framework 


0.85 


Trussed Towers 

Triangular, square, rectangular 
All other cross sections 


0.85 
0.95 



* Directionality Factor Kd has been calibrated with combinations of loads 
specified in Section 2. This factor shall only be applied when used in 
conjunction with load combinations specified in 2.3 and 2.4. 



76 



ASCE 7-02 



SECTION 7,0 

SNOW LOADS 



c e = 

c s = 

c t - 

h b = 

h c — 



h d = 

h e = 

^ = 

/ = 

lu = 

A* = 

Py = 



s — 

= 

w; — 

W = 

y = 



SECTION 7.1 
SYMBOLS AND NOTATIONS 

gable roof drift parameter as determined 

from Eq. 7-3 

exposure factor as determined from Table 7-2 

slope factor as determined from Figure 7-2 

thermal factor as determined from Table 7-3 

height of balanced snow load determined by 

dividing pf or p s by y, in ft (m) 

clear height from top of balanced snow load to 

(1) closest point on adjacent upper roof, (2) top of 

parapet, or (3) top of a projection on the roof, 

in ft (m) 

height of snow drift, in ft (m) 

elevation difference between the ridge line and the 

eaves 

height of obstruction above the surface of the roof, 

in ft (m) 

importance factor as determined from Table 7-4 

length of the roof upwind of the drift, in ft (m) 

maximum intensity of drift surcharge load, in 

pounds per square ft (kn/m 2 ) 

snow load on flat roofs ("flat" — roof slope < 5°), 

in lbs/ft 2 (kn/m 2 ) 

ground snow load as determined from Figure 7-1 

and Table 7-1; or a site-specific analysis, in lbs/ft 2 

(kn/m 2 ) 

sloped roof snow load, in pounds per square 

ft (kn/m 2 ) 

separation distance between buildings, in ft (m) 

roof slope on the leeward side, in degrees 

width of snow drift, in ft (m) 

horizontal distance from eave to ridge, in ft (m) 

snow density, in pounds per cubic ft 

(kn/m 3 ) as determined from Eq. 7-4 



SECTION 7.2 
GROUND SNOW LOADS, p g 

Ground snow loads, p gi to be used in the determination 
of design snow loads for roofs shall be as set forth in 
Figure 7-1 for the contiguous United States and Table 7-1 
for Alaska. Site-specific case studies shall be made to 
determine ground snow loads in areas designated CS in 
Figure 7-1. Ground snow loads for sites at elevations above 
the limits indicated in Figure 7-1 and for all sites within 
the CS areas shall be approved by the authority having 



jurisdiction. Ground snow load determination for such sites 
shall be based on an extreme-value statistical-analysis of 
data available in the vicinity of the site using a value with 
a 2% annual probability of being exceeded (50-year mean 
recurrence interval). 

Snow loads are zero for Hawaii, except in moun- 
tainous regions as determined by the authority having 
jurisdiction. 



SECTION 7.3 
FLAT ROOF SNOW LOADS p f 

The snow load, pf, on a roof with a slope equal to or 
less than 5° (1 in./ft = 4.76°) shall be calculated in lbs/ft 2 
(kn/m 2 ) using the following formula: 



p f ~Q.lC e C t Ip g 



(Eq. 7-1) 



but not less than the following minimum values for low- 
slope roofs as defined in Section 7.3.4: 

where p g is 20 lb/ft 2 (0.96 kN/m 2 ) or less, 

Pf — (I)p g (Importance factor times p g ) 

where p g exceeds 20 lb/ft 2 (0.96 kN/m 2 ), 

Pf = 20(1) (Importance factor times 20 lb/ft 2 ) 

7.3.1 Exposure Factor, C e . The value for C e shall be 
determined from Table 7-2. 

73.2 Thermal Factor, C t . The value for C t shall be 
determined from Table 7-3. 

7.3.3 Importance Factor, L The value for / shall be 
determined from Table 7-4. 

7.3.4 Minimum Values of pf for Low-Slope Roofs. 
Minimum values of pf shall apply to monoslope roofs 
with slopes less than 15 degrees, hip, and gable roofs with 
slopes less than or equal to (70/ W) + 0.5 with W in ft (in 
SI: 21.3/ W 4- 0.5, with W in m), and curved roofs where 
the vertical angle from the eaves to the crown is less than 
10 degrees. 



SECTION 7.4 
SLOPED ROOF SNOW LOADS, p s 

Snow loads acting on a sloping surface shall be assumed to 
act on the horizontal projection of that surface. The sloped 



Minimum Design Loads for Buildings and Other Structures 



77 



roof snow load, p S9 shall be obtained by multiplying the 
flat roof snow load, pf, by the roof slope factor, C s : 



p s = C s p f 



(Eq. 7-2) 



Values of C s for warm roofs, cold roofs, curved roofs, 
and multiple roofs are determined from Sections 7.4.1 
through 7.4.4. The thermal factor, C t , from Table 7-3 
determines if a roof is "cold" or "warm." "Slippery sur- 
face" values shall be used only where the roofs sur- 
face is unobstructed and sufficient space is available 
below the eaves to accept all the sliding snow. A roof 
shall be considered unobstructed if no objects exist on 
it that prevent snow on it from sliding. Slippery sur- 
faces shall include metal, slate, glass, and bituminous, 
rubber, and plastic membranes with a smooth surface. 
Membranes with an imbedded aggregate or mineral granule 
surface shall not be considered smooth. Asphalt shin- 
gles, wood shingles, and shakes shall not be consid- 
ered slippery. 

7.4.1 Warm Roof Slope Factor, C s . For warm roofs 
(C t < 1.0 as determined from Table 7-3) with an 
unobstructed slippery surface that will allow snow to slide 
off the eaves, the roof slope factor C s shall be determined 
using the dashed line in Figure 7-2a, provided that for 
nonventilated warm roofs, their thermal resistance (R- 
value) equals or exceeds 30 ft 2 -hr.°F/Btu (5.3 K-m 2 /W) 
and for warm ventilated roofs, their R-value equals or 
exceeds 20 ft 2 hr F/Btu (3.5 K-m 2 /W). Exterior air shall 
be able to circulate freely under a ventilated roof from 
its eaves to its ridge. For warm roofs that do not meet 
the aforementioned conditions, the solid line in Figure 7-2a 
shall be used to determine the roof slope factor C s . 

1A2 Cold Roof Slope Factor, C s . Cold roofs are those 
with a C, > 1.0 as determined from Table 7-3. For cold 
roofs with C t = 1.1 and an unobstructed slippery surface 
that will allow snow to slide off the eaves, the roof slope 
factor C s shall be determined using the dashed line in 
Figure 7-2b. For all other cold roofs with C t = 1.1, the 
solid line in Figure 7-2b shall be used to determine the 
roof slope factor C s . For cold roofs with C t = 1.2 and 
an unobstructed slippery surface that will allow snow 
to slide off the eaves, the roof slope factor C s shall 
be determined using the dashed line on Figure 7-2c. For 
all other cold roofs with C t — 1.2, the solid line in 
Figure 7-2c shall be used to determine the roof slope 
factor C s . 

7.43 Roof Slope Factor for Curved Roofs. Portions of 
curved roofs having a slope exceeding 70 degrees shall be 
considered free of snow load, (i.e., C s — 0). Balanced loads 
shall be determined from the balanced load diagrams in 



Figure 7-3 with C s determined from the appropriate curve 
in Figure 7-2. 

7.4.4 Roof Slope Factor for Multiple Folded Plate, 
Sawtooth, and Barrel Vault Roofs. Multiple folded plate, 
sawtooth, or barrel vault roofs shall have a C s — 1.0, with 
no reduction in snow load because of slope (i.e., p s — pf). 

7.4.5 Ice Bams and Icicles Along Eaves. Two types 
of warm roofs that drain water over their eaves shall 
be capable of sustaining a uniformly distributed load of 
2pf on all overhanging portions there: those that are 
unventilated and have an R-value less than 30 ft 2 -hr-°F/Btu 
(5.3 k-m 2 /W) and those that are ventilated and have an 
R-value less than 20 ft 2 .hr F/Btu (3.5 k-m 2 /W). No other 
loads except dead loads shall be present on the roof when 
this uniformly distributed load is applied. 

SECTION 7.5 
PARTIAL LOADING 

The effect of having selected spans loaded with the 
balanced snow load and remaining spans loaded with half 
the balanced snow load shall be investigated as follows: 

7.5.1 Continuous Beam Systems. Continuous beam sys- 
tems shall be investigated for the effects of the three load- 
ings shown in Figure 7-4: 

Case 1 : Full balanced snow load on either exterior span 
and half the balanced snow load on all other spans. 

Case 2: Half the balanced snow load on either exterior 
span and full balanced snow load on all other spans. 

Case 3: All possible combinations of full balanced snow 
load on any two adjacent spans and half the balanced 
snow load on all other spans. For this case there will 
be (n — 1) possible combinations where n equals the 
number of spans in the continuous beam system. 

If a cantilever is present in any of the above cases, it shall 
be considered to be a span. 

Partial load provisions need not be applied to structural 
members that span perpendicular to the ridge line in gable 
roofs with slopes greater than 70/ W + 0.5 with W in ft (in 
SI: 21 3/W + 0.5, with W in m). 

7.5.2 Other Structural Systems. Areas sustaining only 
half the balanced snow load shall be chosen so as to produce 
the greatest effects on members being analyzed. 

SECTION 7.6 
UNBALANCED ROOF SNOW LOADS 

Balanced and unbalanced loads shall be analyzed sepa- 
rately. Winds from all directions shall be accounted for 
when establishing unbalanced loads. 



78 



ASCE 7-02 



7.6,1 Unbalanced Snow Loads for Hip and Gable 
Roofs. For hip and gable roofs with a slope exceeding 70° 
or with a slope less than 70/W + 0.5 with W in ft (in 
SI: 21. 3/ W + 0.5, with W in m), unbalanced snow loads 
are not required to be applied. For roofs with an eave to 
ridge distance, W, of 20 ft (6,1 m) or less, the structure 
shall be designed to resist an unbalanced uniform snow 
load on the leeward side equal to 1 3p s /C e . For roofs with 
W > 20 ft (6.1 m), the structure shall be designed to resist 
an unbalanced uniform snow load on the leeward side equal 
to 1.2(1 + p/2)p s /C c with p given by Eq. 7-3. 



In SI: 



1.0 




p g < 20 lb/ft 2 


1.5- 


- 0.025 p g 


20 < p g < 40 lb/ft 2 


0.5 




p, > 40 lb/ft 2 

(Eq. 


1.0 




p g < 0.97 kN/m 2 


1.5- 


- 0.52p, 


0.97 < p g < 1.93 kN/m 2 


0.5 




p g > 1.93 kN/m 2 



For the unbalanced situation with W > 20 ft (6.1 m), the 
windward side shall have a uniform load equal to 03 p s . 
Balanced and unbalanced loading diagrams are presented 
in Figure 7-5. 

7.6.2 Unbalanced Snow Loads for Curved Roofs, 
Portions of curved roofs having a slope exceeding 70 
degrees shall be considered free of snow load. If the slope 
of a straight line from the eaves (or the 70-degree point, 
if present) to the crown is less than 10 degrees or greater 
than 60 degrees, unbalanced snow loads shall not be taken 
into account. 

Unbalanced loads shall be determined according to the 
loading diagrams in Figure 7-3. In all cases the windward 
side shall be considered free of snow. If the ground or 
another roof abuts a Case II or Case III (see Figure 7-3) 
curved roof at or within 3 ft (0.91 m) of its eaves, the 
snow load shall not be decreased between the 30-degree 
point and the eaves but shall remain constant at the 30- 
degree point value. This distribution is shown as a dashed 
line in Figure 7-3. 

7.63 Unbalanced Snow Loads for Multiple Folded 
Plate, Sawtooth, and Barrel Vault Roofs. Unbalanced 
loads shall be applied to folded plate, sawtooth, and bar- 
rel vaulted multiple roofs with a slope exceeding 3/8 in. /ft 
(1.79 degrees). According to 7.4.4, C s = 1.0 for such roofs, 
and the balanced snow load equals pf. The unbalanced 
snow load shall increase from one-half the balanced load 
at the ridge or crown (i.e., 0.5/?/) to two times the bal- 
anced load given in 7.4.4 divided by C e at the valley (i.e., 
2 pf/C e ). Balanced and unbalanced loading diagrams for 
a sawtooth roof are presented in Figure 7-6. However, the 



snow surface above the valley shall not be at an elevation 
higher than the snow above the ridge. Snow depths shall 
be determined by dividing the snow load by the density of 
that snow from Eq. 7-4, which is in Section 7.7.1. 

7.6.4 Unbalanced Snow Loads for Dome Roofs. Unbal- 
anced snow loads shall be applied to domes and similar 
rounded structures. Snow loads, determined in the same 
manner as for curved roofs in Section 7.6.2, shall be applied 
to the downwind 90-degree sector in plan view. At both 
edges of this sector, the load shall decrease linearly to zero 
over sectors of 22.5 degrees each. There shall be no snow 
load on the remaining 225-degree upwind sector. 



SECTION 7.7 

DRIFTS ON LOWER ROOFS 

(AERODYNAMIC SHADE) 

Roofs shall be designed to sustain localized loads from 
snow drifts that form in the wind shadow of (1) higher 
portions of the same structure and, (2) adjacent structures 
and terrain features. 

7.7.1 Lower Roof of a Structure. Snow that forms drifts 
comes from a higher roof or, with the wind from the oppo- 
site direction, from the roof on which the drift is located. 
These two kinds of drifts ("leeward" and "windward," 
respectively) are shown in Figure 7-7. The geometry of the 
surcharge load due to snow drifting shall be approximated 
by a triangle as shown in Figure 7-8. Drift loads shall be 
superimposed on the balanced snow load. If h c / h^ is less 
than 0.2, drift loads are not required to be applied. 

For leeward drifts, the drift height h d shall be determined 
directly from Figure 7-9 using the length of the upper roof. 
For windward drifts, the drift height shall be determined 
by substituting the length of the lower roof for l u in 
Figure 7-9 and using three-quarters of h d as determined 
from Figure 7-9 as the drift height. The larger of these two 
heights shall be used in design. If this height is equal to 
or less than h c , the drift width, w, shall equal 4h d and the 
drift height shall equal h d . If this height exceeds h c , the 
drift width, u>> shall equal Ah 2 d /h c and the drift height shall 
equal h c . However, the drift width, w 9 shall not be greater 
than 8/v If the drift width, w, exceeds the width of the 
lower roof, the drift shall be truncated at the far edge of 
the roof, not reduced to zero there. The maximum intensity 
of the drift surcharge load, p d , equals h d y where snow 
density, y, is defined in Eq. 7-4: 

y = 0A3p g + 14 but not more than 30 pcf (Eq. 7-4) 
(in SI: y = 0A26p g + 2.2 but not more than 4.7 kN/m 3 ) 

This density shall also be used to determine h b by dividing 
Pf (or p s ) by y (in ST. also multiply by 102 to get the 
depth in m). 



Minimum Design Loads for Buildings and Other Structures 



79 



7.7.2 Adjacent Structures and Terrain Features. The 
requirements in Section 7.7.1 shall also be used to deter- 
mine drift loads caused by a higher structure or terrain fea- 
ture within 20 ft (6.1 m) of a roof. The separation distance, 
s, between the roof and adjacent structure or terrain feature 
shall reduce applied drift loads on the lower roof by the fac- 
tor (20 s)/20 where s is in ft [(6.1 s]/6.1 where s is in m). 



SECTION 7.8 
ROOF PROJECTIONS 

The method in Section 7.7.1 shall be used to calculate drift 
loads on all sides of roof projections and at parapet walls. 
The height of such drifts shall be taken as three-quarters the 
drift height from Figure 7-9 (i.e., 0.75 hd) with l u equal to 
the length of the roof upwind of the projection or parapet 
wall. If the side of a roof projection is less than 15 ft (4.6 m) 
long, a drift load is not required to be applied to that side. 



SECTION 7.9 
SLIDING SNOW 

The load caused by snow sliding off a sloped roof onto 
a lower roof shall be determined for slippery upper roofs 
with slopes greater than ~ on 12, and for other (i.e., non- 
slippery) upper roofs with slopes greater than 2 on 12. The 
total sliding load per unit length of eave shall be 0.4/?/ 
W 9 where W is the horizontal distance from the eave to 
ridge for the sloped upper roof. The sliding load shall be 
distributed uniformly on the lower roof over a distance of 
15 ft from the upper roof eave. If the width of the lower 
roof is less than 15 ft, the sliding load shall be reduced 
proportionally. 

The sliding snow load shall not be further reduced unless 
a portion of the snow on the upper roof is blocked from 



sliding onto the lower roof by snow already on the lower 
roof or is expected to slide clear of the lower roof. 

Sliding loads shall be superimposed on the balanced 
snow load. 



SECTION 7.10 
RAIN-ON-SNOW SURCHARGE LOAD 

For locations where p g is 20 lb/ft 2 (0.96 kN/m 2 ) or less but 
not zero, all roofs with a slope less than 1/2 in./ft (2.38°), 
shall have a 5 lb/ft 2 (0.24 kN/m 2 ) rain-on-snow surcharge 
load applied to establish the design snow loads. Where the 
minimum flat roof design snow load from 7.3.4 exceeds pf 
as determined by Eq. 7-1, the rain-on-snow surcharge load 
shall be reduced by the difference between these two values 
with a maximum reduction of 5 lb/ft 2 (0.24 kN/m 2 ). 



SECTION 7.11 
PONDING INSTABILITY 

Roofs shall be designed to preclude ponding instability. 
For roofs with a slope less than 1/4 in./ft (1.19°), roof 
deflections caused by full snow loads shall be investigated 
when determining the likelihood of ponding instability from 
rain-on-snow or from snow meltwater (see Section 8.4). 



SECTION 7.12 
EXISTING ROOFS 

Existing roofs shall be evaluated for increased snow loads 
caused by additions or alterations. Owners or agents for 
owners of an existing lower roof shall be advised of the 
potential for increased snow loads where a higher roof is 
constructed within 20 ft (6.1 m). See footnote to Table 7-2 
and Section 7.7.2. 



80 



ASCE 7-02 



This page intentionally left blank. 



Minimum Design Loads for Buildings and Other Structures 81 



(200) 
20 




In CS areas, site-specific Case Studies are required to 
establish ground snow loads. Extreme local variations 
in ground snow loads in these areas preclude mapping 
at this scale. 

Numbers in parentheses represent the upper elevation 
limits in feet for the ground snow load values presented 
below. Site-specific case studies are required to establish 
ground snow toads at elevations not covered. 



To convert Ib/sq ft to kN/m , multiply by 0.0479, 
To convert feet to meters, multiply by 0.3048. 



300 miles 



FIGURE 7-1 
GROUND SNOW LOADS, p g FOR THE UNITED STATES (IB/SQ FT) 



82 



ASCE 7-02 




>* 



FIGURE 7-1 — continued 
GROUND SNOW LOADS, p g FOR THE UNITED STATES (SB/SQ FT) 



Minimum Design Loads for Buildings and Other Structures 



83 



2 



3 4 6 8 12 
on on on on on 
12 12 12 12 12 



1.0 



0.8 



0.6 



0.4 



0.2 



* 



5'\ 



\ 



\ 



\ 



All 
Other Surfaces 



Unobstructed \ 
Slippery Surfaces 

with R > 30* (5.3**) for 

Unventilated Roofs 
- or R > 20* (3.5**) for 
Ventilated Roofs 

* °F-h-ft 2 /Btu 
** K*rn 2 /W 




3 4 6 8 12 
on on on on on 
12 12 12 12 12 



* 



10°\ 



37.5° 



\ 



\ 



\ 



Unobstructed 
Slippery Surfaces \ 



All — 
\ \ Other Surfaces 

\ 



\ 



\ 



\\ 



3 4 6 8 12 
on on on on on 
12 12 12 12 12 



* 



-y- 
15°\ 



\ 



\ 



\ 



\ 



— Unobstructed 
Slippery Surfaces 




30° 60° 

Roof Slope 



90° 



30° 60° 

Roof Slope 



90° 



30° 



60° 



Roof Slope 



90° 



7-2a: Warm roofs with C t ^1.0 



7~2b: Cold roofs with C t =1 .1 



7~2c: Cold roofs with C t =1 .2 



> 

CO 

o 

m 



FIGURE 7-2 
GRAPHS FOR DETERMINING ROOF SLOPE FACTOR C, FOR WARM AND COLD ROOFS (SEE TABLE 7-3 FOR C, DEFINITIONS) 



o 



Case 1 - Slope at eaves < 30° 



Portion of roof where 
C s = 1 .0 from Figure 7-2 
(may include entire roof) 



Balanced Load 



f-nru i u 1 1 in m-n 



PfC s * 





Eaves 



Wind 



Crown 



Eaves 



Unbalanced Load 



0.5 p f 



Eaves 




2p f C s 7C e 



Case 2 - Slope at eaves 30°to 70° 

Balanced Load B 

Eaves 



Crown 



Portion of roof where 
C s = 1 .0 from Figure 7-2 




! " ♦ t f " 



PfC s ** 



Crown 



Wind 



Unbalanced Load 



0.5 p, 



f~T 



Eaves 



30° 
Point 




Crown 



Case 3 - Slope at eaves > 70° 



Portion of roof where 
C s = 1 .0 from Figure 7-2 



Balanced Load 



Eaves 



t y V 1F v t f t f y f ? t ? 



PfC s 



30° Point Crown 



30° 
Point 



tt 



Eaves 



70° 
Point 



Wind 



70° 
Point 



Unbalanced Load 



0.5 p f 



fTT 



Eaves 



30° 
Point 



70° 
Point 




2p f C s **/C e 



Crown 



Eaves 



* Use the slope at the eaves to determine C s here. 
** Use 30° slope to determine C 5 here. 

♦ Alternate distribution if another roof abuts. 



FIGURE 7-3 
BALANCED AND UNBALANCED LOADS FOR CURVED ROOFS 



Minimum Design Loads for Buildings and Other Structures 



85 



Full 



Half 



1 r 



rrm 



^ , ^_._ _j^i 






Casel 



Full 



Half 



>l^Jl. 



ajti,' ^.ar....: ,:& 



,^....;i;,.-J , ...^..j 



±— iffii 



X-^2; 



A* A 

im/i 



Jk. Jm. 

Case 2 

Full 



Half 



t' : -" :, v; 



....y t,j 



&£IZ± 



ff >■ X! 



I 



Half 



,1,1 






miv 



Case 3 



* The left supports are dashed since they would not exist when a cantilever is present. 



FIGURE 7-4 

PARTIAL LOADING DIAGRAMS FOR CONTINUOUS BEAMS 



86 



ASCE 7-02 




Balanced 



Tl»lT + i»tT?t' 



Unbalanced 
W< 20 ft. (6.1m) 



Unbalanced 
W> 20 ft. (6.1m) 



t » t t t : 



1.5p s /C e 



0.3p s 






j 






1.2(1+(p/2))p s /C e 



Note: Unbalanced loads need not be considered for B> 70° or for 6< 70/W + 0.5 



FIGURE 7-5 
BALANCED AND UNBALANCED SNOW LOADS FOR HIP AND GABLE ROOFS 



Minimum Design Loads for Buildings and Other Structures 



87 



Balanced 
Load 



Unbalanced 
Load 



HM'W 



i^-a^sa 




ini 






,1 

•jpf 

't 



* May be somewhat less; see Section 7.6.3. 



2p f /C e * 



FIGURE 7-6 
BALANCED AND UNBALANCED SNOW LOADS FOR A SAWTOOTH ROOF 



Wind 
Windward Drift 




zur rzy, ;<r~,'\ :.:j:^ 



mm;tm^ ! m^ 



Windward 
Step 



Leeward 
Step 



Leeward Drift 




Snow 



FIGURE 7-7 
DRIFTS FORCED AT WINDWARD AND LEEWARD STEPS 



88 



ASCE 7-02 



-v- 



Pd- 



v ? I ' if . i 




r 



Balanced Snow Load 



v y f u | if y : 7 ir 



W 



FIGURE 7-8 
CONFIGURATION OF SNOW DRIFTS ON LOWER ROOFS 



10 



— If l u > 600 ft, use equation 



8 



X 











h H = 0.43V"7 VPn+10-1-5 



'd v ' u Y ^g 

I I I I I 



20 



40 



60 



80 



100 



p , Ground Snow Load (lb/ft 2 ) 

To convert lb/ft 2 to kN/m 2 , multiply by 0.0479. 
To convert feet to meters, multiply by 0.3048. 



FIGURE 7-9 
GRAPH AND EQUATION FOR DETERMINING DRIFT HEIGHT, h d 



Minimum Design Loads for Buildings and Other Structures 



89 



TABLE 7-1 
GROUND SNOW LOADS, p g , FOR ALASKAN LOCATIONS 





Pg 




Location 




Pg 


Location 




Pg 


Location 


ib/ft 2 


(kN/m 2 ) 


lb/ft 2 


(kN/m 2 ) 


lb/ft 2 


(kN/m 2 ) 


Adak 


30 


(1.4) 


Galena 


60 


(2.9) 


Petersburg 


150 


(7.2) 


Anchorage 


50 


(2.4) 


Gulkana 


70 


(3.4) 


St Paul Islands 


40 


(1.9) 


Angoon 


70 


(3.4) 


Homer 


40 


(1.9) 


Seward 


50 


(2.4) 


Barrow 


25 


(1.2) 


Juneau 


60 


(2.9) 


Shemya 


25 


(1.2) 


Barter Island 


35 


(1.7) 


Kenai 


70 


(3.4) 


Sitka 


50 


(2.4) 


Bethel 


40 


(1.9) 


Kodiak 


30 


(1.4) 


Talkeetna 


120 


(5.8) 


Big Delta 


50 


(2.4) 


Kotzebue 


60 


(2.9) 


Unalakleet 


50 


(2.4) 


Cold Bay 


25 


(1.2) 


McGrath 


70 


(3.4) 


Valdez 


160 


(7.7) 


Cordova 


100 


(4.8) 


Nenana 


80 


(3.8) 


Whittier 


300 


(14.4) 


Fairbanks 


60 


(2.9) 


Nome 


70 


(3.4) 


Wrangell 


60 


(2.9) 


Fort Yukon 


60 


(2.9) 


Palmer 


50 


(2.4) 


Yakutat 


150 


(7.2) 










TABLE 7-2 
















EXPOSURE FACTOR, C e 


















Fully 


Exposure of Roof* 










Terrain Category 




Exposed 


Partially Exposed 


Sheltered 






A (see Section 6.5.6) 






N/A 


1.1 


1.3 






B (see Section 6.5.6) 






0.9 


1.0 


1.2 






C (see Section 6.5.6) 






0.9 


1.0 


1.1 






D (see Section 6.5.6) 






0.8 


0.9 


1.0 






Above the treeline 


: in windswept 


t mountainous 


areas. 


0.7 


0.8 


N/A. 






In Alaska, in areas 


s where trees do not exist within a 


0.7 


0.8 


N/A 






2-mile (3 km) radi 


ins of the site. 















The terrain category and roof exposure condition chosen shall be representative of the anticipated conditions during 
the life of the structure. An exposure factor shall be determined for each roof of a structure. 

* Definitions 

PARTIALLY EXPOSED. All roofs except as indicated below. 

FULLY EXPOSED. Roofs exposed on all sides with no shelter** afforded by terrain, higher structures, or trees. Roofs 
that contain several large pieces of mechanical equipment, parapets that extend above the height of the balanced snow 
load (hb), or other obstructions are not in this category. 

SHELTERED. Roofs located tight in among conifers that qualify as obstructions. 

** Obstructions within a distance of 10h o provide ''shelter," where h is the height of the obstruction above the roof 
level. If the only obstructions are a few deciduous trees that are leafless in winter, the "fully exposed" category shall be 
used except for terrain Category "A." Note that these are heights above the roof. Heights used to establish the terrain 
category in Section 6.5.3 are heights above the ground. 



90 



ASCE 7-02 



TABLE 7-3 
THERMAL FACTOR, C t 



Thermal Condition* 



All structures except as indicated below 1.0 

Structures kept just above freezing and others with cold, ventilated roofs in 1.1 

which the thermal resistance (R- value) between the ventilated space and the 
heated space exceeds 25 F°-hr-sq ft/Btu (4.4 K-m 2 /W) 

Unheated structures and structures intentionally kept below freezing 1.2 

Continuously heated greenhouses** with a roof having a thermal resistance 0.85 

(R- value) less than 2.0 F°.hr-ft 2 /Btu(0.4 K-m 2 AV) 

* These conditions shall be representative of the anticipated conditions during winters for the life of 
the structure. 

** Greenhouses with a constantly maintained interior temperature of 50 °F (10 °C) or more at any 
point 3 ft above the floor level during winters and having either a maintenance attendant on duty at 
all times or a temperature alarm system to provide warning in the event of a heating failure. 



TABLE 7-4 

IMPORTANCE FACTOR, 

/, (SNOW LOADS) 

Category* / 

I 0.8 

II 1.0 

III 1.1 

IV 1.2 

*See Section 1.5 and Table 1-1. 



Minimum Design Loads for Buildings and Other Structures 91 



section ao 

RAIN LOADS 



SECTION 8.1 
SYMBOLS AND NOTATION 

R — rain load on the undeflected roof, in pounds per 
square ft (kilonewtons/m 2 ). When the phrase 
"undeflected roof is used, deflections from loads 
(including dead loads) shall not be considered when 
determining the amount of rain on the roof. 

d s = depth of water on the undeflected roof up to the 
inlet of the secondary drainage system when the 
primary drainage system is blocked (i.e., the static 
head), in in. (mm). 

dh — additional depth of water on the undeflected roof 
above the inlet of the secondary drainage system at 
its design flow (i.e., the hydraulic head), in in. (mm). 

SECTION 8.2 
ROOF DRAINAGE 

Roof drainage systems shall be designed in accordance with 
the provisions of the code having jurisdiction. The flow 
capacity of secondary (overflow) drains or scuppers shall 
not be less than that of the primary drains or scuppers. 

SECTION 8.3 
DESIGN RAIN LOADS 

Each portion of a roof shall be designed to sustain the load 
of all rainwater that will accumulate on it if the primary 
drainage system for that portion is blocked plus the uniform 
load caused by water that rises above the inlet of the 
secondary drainage system at its design flow. 



If the secondary drainage systems contain drain lines, such 
lines and their point of discharge shall be separate from the 
primary drain lines. 



SECTION 8.4 
PONDING INSTABILITY 

"Ponding" refers to the retention of water due solely to 
the deflection of relatively flat roofs. Roofs with a slope 
less than 1/4 in./ft (1.19 degrees) shall be investigated by 
structural analysis to ensure that they possess adequate stiff- 
ness to preclude progressive deflection (i.e., instability) as 
rain falls on them or meltwater is created from snow on 
them. The larger of snow load or rain load shall be used in 
this analysis. The primary drainage system within an area 
subjected to ponding shall be considered to be blocked in 
this analysis. 



SECTION 8.5 
CONTROLLED DRAINAGE 

Roofs equipped with hardware to control the rate of 
drainage shall be equipped with a secondary drainage 
system at a higher elevation that limits accumulation of 
water on the roof above that elevation. Such roofs shall 
be designed to sustain the load of all rainwater that will 
accumulate on them to the elevation of the secondary 
drainage system, plus the uniform load caused by water 
that rises above the inlet of the secondary drainage system 
at its design flow (determined from Section 8.3). 

Such roofs shall also be checked for ponding instability 
(determined from Section 8.4). 



R = 5.2(d s +d h ) 

In SI: R = 0.Q09&(d s +d h ) 



(Eq. 8-1) 



Minimum Design Loads for Buildings and Other Structures 



93 



SECTION 9.0 

EARTHQUAKE LOADS 



[Note to user: This Section is based on the 2000 NEHRP 
Recommended Provisions for the Development of Seismic 
Regulations for New Buildings.] 



SECTION 9.1 
GENERAL PROVISIONS 

9.1.1 Purpose. Section 9 presents criteria for the design 
and construction of buildings and similar structures subject 
to earthquake ground motions. The specified earthquake 
loads are based on post-elastic energy dissipation in the 
structure, and because of this fact, the provisions for 
design, detailing, and construction shall be satisfied even 
for structures and members for which load combinations 
that do not contain the earthquake effect indicate larger 
demands than combinations including earthquake. 

9.1.2 Scope and Application. 

9.1.2.1 Scope. Every building, and portion thereof, 
shall be designed and constructed to resist the effects 
of earthquake motions as prescribed by these provi- 
sions. Certain nonbuilding structures, as described in 
Section 9.14, are within the scope and shall be designed 
and constructed as required for buildings. Additions to 
existing structures also shall be designed and constructed 
to resist the effects of earthquake motions as prescribed 
by these provisions. Existing structures and alterations 
to existing structures need only comply with these pro- 
visions when required by Sections 9.1.2.2 and 9.1.2.3. 

Exceptions: 

1. Structures located where the mapped spectral 
response acceleration at 1-sec period, Si, is 
less than or equal to 0.04 g and the mapped 
short period spectral response acceleration, Ss, 
is less than or equal to 0.15 g shall only be 
required to comply with Section 9.5.2.6.1. 

2. Detached one- and two-family dwellings that 
are located where the mapped, short period, 
spectral response acceleration, Ss, is less than 
0.4 g or where the Seismic Design Category 
determined in accordance with Section 9.4.2 is 
A, B, or C are exempt from the requirements 
of these provisions. 

3. Detached one- and two-family wood frame 
dwellings not included in Exception 2 with 



not more than 2 stories and satisfying the 
limitations of International Code Council (ICC) 
[Ref. 9.12-10] are only required to be con- 
structed in accordance with Ref. 9.12-10. 

4. Agricultural storage structures that are intended 
only for incidental human occupancy are 
exempt from the requirements of these provi- 
sions. 

Special structures including, but not limited to, vehic- 
ular bridges, transmission towers, piers and wharves, 
hydraulic structures, and nuclear reactors require special 
consideration of their response characteristics and envi- 
ronment that is beyond the scope of these provisions. 

9.1.2.2 Additions to Existing Structures. Additions 
shall be made to existing structures only as follows: 

9.1.2.2.1 An addition that is structurally independent 
from an existing structure shall be designed and con- 
structed in accordance with the seismic requirements 
for new structures. 

9.1.2.2.2 An addition that is not structurally indepen- 
dent from an existing structure shall be designed and 
constructed such that the entire structure conforms 
to the seismic force-resistance requirements for new 
structures unless the following three conditions are 
complied with: 

1. The addition shall comply with the require- 
ments for new structures. 

2. The addition shall not increase the seismic 
forces in any structural element of the existing 
structure by more than 5% unless the capacity 
of the element subject to the increased forces is 
still in compliance with these provisions. 

3. The addition shall not decrease the seismic 
resistance of any structural element of the 
existing structure unless the reduced resistance 
is equal to or greater than that required for 
new structures. 

9.1.2.3 Change of Use. When a change of use results 
in a structure being reclassified to a higher Seismic 
Use Group, the structure shall conform to the seismic 
requirements for new construction. 



Minimum Design Loads for Buildings and Other Structures 



95 



Exceptions: 



TABLE 9.1.3 
SEISMIC USE GROUP 



1. When a change of use results in a structure 
being reclassified from Seismic Use Group I 
to Seismic Use Group II and the structure is 
located in a seismic map area where Sds < 
0.33, compliance with these provisions is 
not required. 

2. Specific seismic detailing provisions of 
Appendix A required for a new structure are 
not required to be met when it can be shown 
that the level of performance and seismic safety 
is equivalent to that of a new structure. Such 
analysis shall consider the regularity, over- 
strength, redundancy, and ductility of the struc- 
ture within the context of the existing and 
retrofit (if any) detailing provided. 



9.1.2.4 Application of Provisions. Buildings and struc- 
tures within the scope of these provisions shall be 
designed and constructed as required by this Section. 
When required by the authority having jurisdiction, 
design documents shall be submitted to determine com- 
pliance with these provisions. 

9,1.2.4.1 New Buildings. New buildings and struc- 
tures shall be designed and constructed in accor- 
dance with the quality assurance requirements of 
Section 9.4.3. The analysis and design of structural 
systems and components, including foundations, 
frames, walls, floors, and roofs shall be in accordance 
with the applicable requirements of Sections 9.5 and 
9.7. Materials used in construction and components 
made of these materials shall be designed and con- 
structed to meet the requirements of Sections 9.8 
through 9.12. Architectural, electrical, and mechan- 
ical systems and components including tenant 
improvements shall be designed in accordance with 
Section 9.6. 

9.1.2.5 Alternate Materials and Methods of Con- 
struction. Alternate materials and methods of construc- 
tion to those prescribed in these provisions shall not be 
used unless approved by the authority having jurisdic- 
tion. Substantiating evidence shall be submitted demon- 
strating that the proposed alternate, for the purpose 
intended, will be at least equal in strength, durability, 
and seismic resistance. 

9.1.3 Seismic Use Groups. All structures shall be assigned 
to Seismic Use Group: I, II, or III as specified in Table 9.1.3 
corresponding to its Occupancy Category determined from 
Table 1-1: 

9.13.1 High Hazard Exposure Structures. All build- 
ings and structures assigned to Seismic Use Group III 
shall meet the following requirements: 







Seismic Use Group 




I 


II 


III 


Occupancy 
Category 
(Table 1-1) 


I 


X 






II 


X 






III 




X 




IV 






X 



9.1.3.1.1 Seismic Use Group III Structure Pro- 
tected Access. Where operational access to a Seismic 
Use Group III structure is required through an adja- 
cent structure, the adjacent structure shall conform 
to the requirements for Seismic Use Group III struc- 
tures. Where operational access is less than 10 ft from 
the interior lot line or another structure on the same 
lot, protection from potential falling debris from adja- 
cent structures shall be provided by the owner of the 
Seismic Use Group III structure. 

9.1.3.1.2 Seismic Use Group III Function. Desig- 
nated seismic systems in Seismic Use Group III struc- 
tures shall be provided with the capacity to function, 
in so far as practical, during and after an earthquake. 
Site-specific conditions as specified in Section 9.6.3.8 
that could result in the interruption of utility services 
shall be considered when providing the capacity to 
continue to function. 

9.1.3.2 This Section is intentionally left blank. 

9.1.3.3 This Section is intentionally left blank. 

9.1.3.4 Multiple Use. Structures having multiple uses 
shall be assigned the classification of the use having the 
highest Seismic Use Group except in structures having 
two or more portions which are structurally separated 
in accordance with Section 9.5.2.8, each portion shall 
be separately classified. Where a structurally separated 
portion of a structure provides access to, egress from, 
or shares life safety components with another portion 
having a higher Seismic Use Group, both portions shall 
be assigned the higher Seismic Use Group. 

9.1.4 Occupancy Importance Factor. An occupancy 
importance factor, I, shall be assigned to each structure 
in accordance with Table 9.1.4. 

9.2.1 Definitions, The definitions presented in this Section 
provide the meaning of the terms used in these provisions. 
Definitions of terms that have a specific meaning relative to 



96 



ASCE 7-02 



TABLE 9.1.4 

OCCUPANCY IMPORTANCE 

FACTORS 



Seismic Use Group 


/ 


I 


1.0 


II 


1.25 


III 


1.5 



the use of wood, steel, concrete, or masonry are presented in 
the section devoted to the material (Sections A. 9. 8 through 
A.9.12, respectively). 

ACTIVE FAULT, A fault determined to be active by the 
authority having jurisdiction from properly substantiated 
geotechnical data (e.g., most recent mapping of active faults 
by the U.S. Geological Survey). 

ADDITION. An increase in building area, aggregate floor 
area, height, or number of stories of a structure. 

ADJUSTED RESISTANCE (/)')• The reference resis- 
tance adjusted to include the effects of all applicable adjust- 
ment factors resulting from end-use and other modifying 
factors. Time effect factor (A) adjustments are not included. 

ALTERATION. Any construction or renovation to an 
existing structure other than an addition. 

APPENDAGE. An architectural component such as a 
canopy, marquee, ornamental balcony, or statuary. 

APPROVAL. The written acceptance by the authority 
having jurisdiction of documentation that establishes the 
qualification of a material, system, component, procedure, 
or person to fulfill the requirements of these provisions for 
the intended use. 

ARCHITECTURAL COMPONENT SUPPORT. Those 
structural members or assemblies of members, including 
braces, frames, struts, and attachments that transmit all 
loads and forces between architectural systems, compo- 
nents, or elements and the structure. 

ATTACHMENTS. Means by which components and their 
supports are secured or connected to the seismic force- 
resisting system of the structure. Such attachments include 
anchor bolts, welded connections, and mechanical fasteners. 

BASE. The level at which the horizontal seismic ground 
motions are considered to be imparted to the structure. 

BASE SHEAR. Total design lateral force or shear at 
the base. 

BASEMENT. A basement is any story below the lowest 
story above grade. 



BOUNDARY ELEMENTS. Diaphragm and shear wall 
boundary members to which the diaphragm transfers forces. 
Boundary members include chords and drag struts at 
diaphragm and shear wall perimeters, interior openings, 
discontinuities, and re-entrant corners. 

BOUNDARY MEMBERS. Portions along wall and 
diaphragm edges strengthened by longitudinal and 
transverse reinforcement. Boundary members include 
chords and drag struts at diaphragm and shear wall 
perimeters, interior openings, discontinuities, and re-entrant 
corners. 

BUILDING. Any structure whose use could include shel- 
ter of human occupants. 

CANTILEVERED COLUMN SYSTEM. A seismic 
force-resisting system in which lateral forces are 
resisted entirely by columns acting as cantilevers from 
the foundation. 

COMPONENT. A part or element of an architectural, 
electrical, mechanical, or structural system. 

Component, equipment. A mechanical or electrical 
component or element that is part of a mechanical and/or 
electrical system within or without a building system. 

Component, flexible. Component, including its attach- 
ments, having a fundamental period greater than 
0.06 sec. 

Component, rigid. Component, including its attach- 
ments, having a fundamental period less than or equal 
to 0.06 sec. 

CONCRETE, PLAIN. Concrete that is either unrein- 
forced or contains less reinforcement than the minimum 
amount specified in Ref. 9.9-1 for reinforced concrete. 

CONCRETE, REINFORCED. Concrete reinforced with 
no less than the minimum amount required by Ref. 9.9-1, 
prestressed or nonprestressed, and designed on the assump- 
tion that the two materials act together in resisting forces. 

CONFINED REGION. That portion of a reinforced con- 
crete or reinforced masonry component in which the 
concrete or masonry is confined by closely spaced spe- 
cial transverse reinforcement restraining the concrete or 
masonry in directions perpendicular to the applied stress. 

CONSTRUCTION DOCUMENTS. The written, graphic, 
electronic, and pictorial documents describing the design, 
locations, and physical characteristics of the project required 
to verify compliance with this Standard. 

CONTAINER. A large-scale independent component used 
as a receptacle or vessel to accommodate plants, refuse, or 
similar uses, not including liquids. 



Minimum Design Loads for Buildings and Other Structures 



97 



COUPLING BEAM. A beam that is used to connect 
adjacent concrete wall elements to make them act together 
as a unit to resist lateral loads. 

DEFORMABILITY. The ratio of the ultimate deforma- 
tion to the limit deformation. 

High deformability element An element whose 
deformability is not less than 3.5 when subjected to four 
fully reversed cycles at the limit deformation. 

Limited deformability element An element that is 
neither a low deformability nor a high deformabil- 
ity element. 

Low deformability element An element whose deform- 
ability is 1.5 or less. 

DEFORMATION. 

Limit deformation. Two times the initial deforma- 
tion that occurs at a load equal to 40% of the maxi- 
mum strength. 

Ultimate deformation. The deformation at which fail- 
ure occurs and which shall be deemed to occur if the 
sustainable load reduces to 80% or less of the maxi- 
mum strength. 

DESIGN EARTHQUAKE GROUND MOTION. The 
earthquake effects that buildings and structures are specifi- 
cally proportioned to resist as defined in Section 9.4.1. 

DESIGN EARTHQUAKE. The earthquake effects that 
are two-thirds of the corresponding maximum consid- 
ered earthquake. 

DESIGNATED SEISMIC SYSTEMS. The seismic force- 
resisting system and those architectural, electrical, and 
mechanical systems or their components that require design 
in accordance with Section 9.6.1 and for which the compo- 
nent importance factor, I p , is >1.0. 

DIAPHRAGM. Roof, floor, or other membrane or brac- 
ing system acting to transfer the lateral forces to the 
vertical resisting elements. Diaphragms are classified as 
either flexible or rigid according to the requirements of 
Section 9.5.2.3.1. 

DIAPHRAGM, BLOCKED. A diaphragm in which all 
sheathing edges not occurring on a framing member are 
supported on and fastened to blocking. 

DIAPHRAGM BOUNDARY. A location where shear is 
transferred into or out of the diaphragm element. Transfer 
is either to a boundary element or to another force- 
resisting element. 

DIAPHRAGM CHORD. A diaphragm boundary element 
perpendicular to the applied load that is assumed to take 
axial stresses due to the diaphragm moment in a manner 



analogous to the flanges of a beam. Also applies to 
shear walls. 

DISPLACEMENT. 

Design displacement. The design earthquake lateral 
displacement, excluding additional displacement due to 
actual and accidental torsion, required for design of the 
isolation system. 

Total design displacement. The design earthquake lat- 
eral displacement, including additional displacement due 
to actual and accidental torsion, required for design of 
the isolation system or an element thereof. 

Total maximum displacement. The maximum consid- 
ered earthquake lateral displacement, including addi- 
tional displacement due to actual and accidental torsion, 
required for verification of the stability of the isolation 
system or elements thereof, design of structure separa- 
tions, and vertical load testing of isolator unit prototypes, 

DISPLACEMENT RESTRAINT SYSTEM. A collec- 
tion of structural elements that limits lateral displacement 
of seismically isolated structures due to the maximum con- 
sidered earthquake. 

DRAG STRUT (COLLECTOR, TIE, DIAPHRAGM 
STRUT). A diaphragm or shear wall boundary element 
parallel to the applied load that collects and transfers 
diaphragm shear forces to the vertical-force-resisting ele- 
ments or distributes forces within the diaphragm or shear 
wall. A drag stmt often is an extension of a boundary ele- 
ment that transfers forces into the diaphragm or shear wall. 
See Sections 9.5.2.6.3.1 and 9.5.2.6.4.1. 

EFFECTIVE DAMPING. The value of equivalent vis- 
cous damping corresponding to energy dissipated during 
cyclic response of the isolation system. 

EFFECTIVE STIFFNESS. The value of the lateral force 
in the isolation system, or an element thereof, divided by 
the corresponding lateral displacement. 

ENCLOSURE. An interior space surrounded by walls. 

EQUIPMENT SUPPORT. Those structural members or 
assemblies of members or manufactured elements, includ- 
ing braces, frames, legs, lugs, snuggers, hangers, or saddles, 
that transmit gravity loads and operating loads between the 
equipment and the structure. 

ESSENTIAL FACILITY. A structure required for post- 
earthquake recovery. 

FACTORED RESISTANCE (A.0D). Reference resistance 
multiplied by the time effect and resistance factors. This 
value must be adjusted for other factors such as size effects, 
moisture conditions, and other end-use factors. 



98 



ASCE 7-02 



FLEXIBLE EQUIPMENT CONNECTIONS. Those 
connections between equipment components that permit 
rotational and/or translational movement without degrada- 
tion of performance. Examples include universal joints, 
bellows expansion joints, and flexible metal hose. 

FRAME. 

Braced frame. An essentially vertical truss, or its 
equivalent, of the concentric or eccentric type that is 
provided in a bearing wall, building frame, or dual 
system to resist seismic forces. 

Concentrically braced frame (CBF). A braced 
frame in which the members are subjected primarily 
to axial forces. 

Eccentrically braced frame (EBF). A diagonally 
braced frame in which at least one end of each brace 
frames into a beam a short distance from a beam- 
column joint or from another diagonal brace. 

Ordinary concentrically braced frame (OCBF). A 
steel concentrically braced frame in which members 
and connections are designed in accordance with the 
provisions of Ref. 9.8-3 without modification. 

Special concentrically braced frame (SCBF). A 
steel or composite steel and concrete concentrically 
braced frame in which members and connections are 
designed for ductile behavior. Special concentrically 
braced frames shall conform to Section A. 9. 8. 1.3.1. 

Moment frame. 

Intermediate moment frame (IMF). A moment 
frame in which members and joints are capable 
of resisting forces by flexure as well as along the 
axis of the members. Intermediate moment frames 
of reinforced concrete shall conform to Ref. 9.9-1. 
Intermediate moment frames of structural steel con- 
struction shall conform to Section 9.8-3 or 10. Inter- 
mediate moment frames of composite construction 
shall conform to Ref. 9.10-3, Part II, Section 6.4b, 7, 
8, and 10. 

Ordinary moment frame (OMF). A moment frame 
in which members and joints are capable of resisting 
forces by flexure as well as along the axis of the 
members. Ordinary moment frames shall conform to 
Ref. 9.9-1, exclusive of Chapter 21, and Ref. 9.8-3, 
Section 12 or A.9.9.3.L 

Special moment frame (SMF). A moment frame in 
which members and joints are capable of resisting 
forces by flexure as well as along the axis of the 
members. Special moment frames shall conform to 
Ref. 9.8-3 or Ref. 9.9-1. 



FRAME SYSTEM. 

Building frame system. A structural system with an 
essentially complete space frame providing support for 
vertical loads. Seismic force resistance is provided by 
shear walls or braced frames. 

Dual frame system. A structural system with an essen- 
tially complete space frame providing support for ver- 
tical loads. Seismic force resistance is provided by 
moment-resisting frames and shear walls or braced 
frames as prescribed in Section 9.5.2.2.1. 

Space frame system. A structural system composed of 
interconnected members, other than bearing walls, that is 
capable of supporting vertical loads and, when designed 
for such an application, is capable of providing resistance 
to seismic forces. 

GLAZED CURTAIN WALL. A nonbearing wall that 
extends beyond the edges of building floor slabs and 
includes a glazing material installed in the curtain 
wall framing. 

GLAZED STOREFRONT. A nonbearing wall that is 
installed between floor slabs, typically including entrances, 
and includes a glazing material installed in the store- 
front framing. 

GRADE PLANE. A reference plane representing the aver- 
age of finished ground level adjoining the structure at all 
exterior walls. Where the finished ground level slopes away 
from the exterior walls, the reference plane shall be estab- 
lished by the lowest points within the area between the 
buildings and the lot line or, where the lot line is more 
than 6 ft (1829 mm) from the structure, between the struc- 
ture and a point 6 ft (1829 mm) from the structure. 

HAZARDOUS CONTENTS. A material that is highly 
toxic or potentially explosive and in sufficient quantity to 
pose a significant life safety threat to the general public if 
an uncontrolled release were to occur, 

HIGH TEMPERATURE ENERGY SOURCE. A fluid, 
gas, or vapor whose temperature exceeds 220 °F. 

INSPECTION, SPECIAL. The observation of the work 
by the special inspector to determine compliance with the 
approved construction documents and these standards. 

Continuous special inspection. The full-time observa- 
tion of the work by an approved special inspector who 
is present in the area where work is being performed. 

Periodic special inspection. The part-time or intermit- 
tent observation of the work by an approved special 
inspector who is present in the area where work has 
been or is being performed. 

INSPECTOR, SPECIAL (WHO SHALL BE IDENTI- 
FIED AS THE OWNER'S INSPECTOR). A person 



Minimum Design Loads for Buildings and Other Structures 



99 



approved by the authority having jurisdiction to perform 
special inspection. The authority having jurisdiction shall 
have the option to approve the quality assurance personnel 
of a fabricator as a special inspector. 

INVERTED PENDULUM-TYPE STRUCTURES. 
Structures that have a large portion of their mass concen- 
trated near the top and, thus, have essentially one degree of 
freedom in horizontal translation. The structures are usu- 
ally T-shaped with a single column supporting the beams 
or framing at the top. 

ISOLATION INTERFACE, The boundary between the 
upper portion of the structure, which is isolated, and the 
lower portion of the structure, which moves rigidly with 
the ground. 

ISOLATION SYSTEM. The collection of structural ele- 
ments that includes all individual isolator units, all struc- 
tural elements that transfer force between elements of the 
isolation system, and all connections to other structural ele- 
ments. The isolation system also includes the wind-restraint 
system, energy-dissipation devices, and/or the displacement 
restraint system if such systems and devices are used to 
meet the design requirements of Section 9.13. 

ISOLATOR UNIT. A horizontally flexible and vertically 
stiff structural element of the isolation system that permits 
large lateral deformations under design seismic load. An 
isolator unit may be used either as part of or in addition to 
the weight-supporting system of the structure. 

JOINT. The geometric volume common to intersect- 
ing members. 

LIGHT-FRAME CONSTRUCTION. A method of con- 
struction where the structural assemblies (e.g., walls, floors, 
ceilings, and roofs) are primarily formed by a system of 
repetitive wood or cold-formed steel framing members or 
subassemblies of these members (e.g., trusses). 

LOAD. 

Dead load. The gravity load due to the weight of all 
permanent structural and nonstructural components of a 
building such as walls, floors, roofs, and the operating 
weight of fixed service equipment. 

Gravity load (W). The total dead load and applicable 
portions of other loads as defined in Section 9.53. 

Live load. The load superimposed by the use and 
occupancy of the building not including the wind load, 
earthquake load, or dead load, see Section 9.5.3. 

MAXIMUM CONSIDERED EARTHQUAKE 

GROUND MOTION. The most severe earthquake effects 
considered by these standards as defined in Section 9.4.1. 



NONBUILDING STRUCTURE. A structure, other than 
a building, constructed of a type included in Section 9.14 
and within the limits of Section 9.14.1.1. 

OCCUPANCY IMPORTANCE FACTOR. A factor 
assigned to each structure according to its Seismic Use 
Group as prescribed in Section 9.1.4. 

OWNER. Any person, agent, firm, or corporation having 
a legal or equitable interest in the property. 

PARTITION. A nonstructural interior wall that spans hor- 
izontally or vertically from support to support. The supports 
may be the basic building frame, subsidiary structural mem- 
bers, or other portions of the partition system. 

P -DELTA EFFECT. The secondary effect on shears and 
moments of structural members due to the action of the 
vertical loads induced by displacement of the structure 
resulting from various loading conditions. 

QUALITY ASSURANCE PLAN. A detailed written pro- 
cedure that establishes the systems and components subject 
to special inspection and testing. The type and frequency 
of testing and the extent and duration of special inspection 
are given in the quality assurance plan. 

REFERENCE RESISTANCE (D). The resistance (force 
or moment as appropriate) of a member or connection 
computed at the reference end-use conditions. 

REGISTERED DESIGN PROFESSIONAL. An archi- 
tect or engineer, registered or licensed to practice pro- 
fessional architecture or engineering, as defined by the 
statutory requirements of the professional registrations laws 
of the state in which the project is to be constructed. 

ROOFING UNIT. A unit of roofing tile or similar material 
weighing more than 1 pound. 

SEISMIC DESIGN CATEGORY. A classification as- 
signed to a structure based on its Seismic Use Group and 
the severity of the design earthquake ground motion at the 
site as defined in Section 9.4.2. 

SEISMIC FORCE-RESISTING SYSTEM. That part of 
the structural system that has been considered in the design 
to provide the required resistance to the seismic forces 
prescribed herein. 

SEISMIC FORCES. The assumed forces prescribed 
herein, related to the response of the structure to earthquake 
motions, to be used in the design of the structure and 
its components. 

SEISMIC RESPONSE COEFFICIENT. Coefficient C s 
as determined from Section 9.5.5.2.1. 

SEISMIC USE GROUP. A classification assigned to a 
structure based on its use as defined in Section 9.1.3. 



100 



ASCE 7-02 



SHALLOW ANCHOR. Anchors with embedment length- 
to-diameter ratios of less than 8. 

SHEAR PANEL. A floor, roof, or wall component 
sheathed to act as a shear wall or diaphragm. 

SITE CLASS. A classification assigned to a site based on 
the types of soils present and their engineering properties 
as defined in Section 9.4.1.2. 

SITE COEFFICIENTS. The values of F Q and F v as 
indicated in Tables 9.4.1.2.4a and 9.4.1.2.4b, respectively. 

SPECIAL TRANSVERSE REINFORCEMENT. Rein- 
forcement composed of spirals, closed stirrups, or hoops 
and supplementary crossties provided to restrain the con- 
crete and qualify the portion of the component, where used, 
as a confined region. 

STORAGE RACKS. Include industrial pallet racks, 
moveable shelf racks, and stacker racks made of cold- 
formed or hot-rolled structural members. Does not include 
other types of racks such as drive-in and drive-through 
racks, cantilever racks, portable racks, or racks made of 
materials other than steel. 

STORY. The portion of a structure between the top of 
two successive, finished floor surfaces and, for the topmost 
story, from the top of the floor finish to the top of the roof 
structural element. 

STORY ABOVE GRADE. Any story having its finished 
floor surface entirely above grade, except that a story shall 
be considered as a story above grade where the finished 
floor surface of the story immediately above is more than 
6 ft (1829 mm) above the grade plane, more than 6 ft 
(1829 mm) above the finished ground level for more than 
40% of the total structure perimeter, or more than 12 ft 
(3658 mm) above the finished ground level at any point. 

STORY DRIFT. The difference of horizontal deflections 
at the top and bottom of the story as determined in 
Section 9.5.5.7.1. 

STORY DRIFT RATIO. The story drift, as determined in 
Section 9.5.5.7.1, divided by the story height. 

STORY SHEAR. The summation of design lateral seismic 
forces at levels above the story under consideration. 

STRENGTH. 

Design strength. Nominal strength multiplied by a 
strength reduction factor, </>. 

Nominal strength. Strength of a member or cross- 
section calculated in accordance with the requirements 
and assumptions of the strength design methods of this 
Standard (or the referenced standards) before application 
of any strength reduction factors. 



Required strength. Strength of a member, cross-section, 
or connection required to resist factored loads or related 
internal moments and forces in such combinations as 
stipulated by this Standard. 

STRUCTURE. That which is built or constructed and 
limited to buildings and nonbuilding structures as 
defined herein. 

STRUCTURAL OBSERVATIONS. The visual observa- 
tions performed by the registered design professional in 
responsible charge (or another registered design profes- 
sional) to determine that the seismic force-resisting system 
is constructed in general conformance with the construc- 
tion documents. 

STRUCTURAL-USE PANEL. A wood-based panel prod- 
uct that meets the requirements of Ref. 9.12-3 or Ref. 9.12- 
5 and is bonded with a waterproof adhesive. Included under 
this designation are plywood, oriented strand board, and 
composite panels. 

SUBDIAPHRAGM. A portion of a diaphragm used to 
transfer wall anchorage forces to diaphragm crossties. 

TESTING AGENCY. A company or corporation that 
provides testing and/or inspection services. The person in 
charge of the special inspector(s) and the testing services 
shall be a registered design professional. 

TIE-DOWN (HOLD-DOWN). A device used to resist 
uplift of the boundary elements of shear walls. These 
devices are intended to resist load without significant slip 
between the device and the shear wall boundary element or 
be shown with cyclic testing to not reduce the wall capacity 
or ductility. 

TIME EFFECT FACTOR (A). A factor applied to the 
adjusted resistance to account for effects of duration 
of load. 

TORSIONAL FORCE DISTRIBUTION. The distribu- 
tion of horizontal shear through a rigid diaphragm when the 
center of mass of the structure at the level under considera- 
tion does not coincide with the center of rigidity (sometimes 
referred to as diaphragm rotation). 

TOUGHNESS. The ability of a material to absorb energy 
without losing significant strength. 

UTILITY OR SERVICE INTERFACE. The connection 
of the structure's mechanical and electrical distribution sys- 
tems to the utility or service company's distribution system. 

VENEERS. Facings or ornamentation of brick, concrete, 
stone, tile, or similar materials attached to a backing. 

WALL. A component that has a slope of 60 degrees 
or greater with the horizontal plane used to enclose or 
divide space. 



Minimum Design Loads for BuiBdings and Other Structures 



101 



Bearing wall. Any wall meeting either of the following 
classifications: 

1. Any metal or wood stud wall that supports more 
than 100 pounds per linear ft (1459 N/m) of ver- 
tical load in addition to its own weight. 

2. Any concrete or masonry wall that supports more 
than 200 pounds per linear ft (2919 N/m) of ver- 
tical load in addition to its own weight. 

Cripple wall. Short stud wall, less than 8 ft (2400 mm) 
in height, between the foundation and the lowest framed 
floors with studs not less than 14 inches long — also 
known as a knee wall. Cripple walls can occur in both 
engineered structures and conventional construction. 

Light-framed wall. A wall with wood or steel studs. 

Light-framed wood shear wall. A wall constructed 
with wood studs and sheathed with material rated for 
shear resistance. 

Nonbearing wall. Any wall that is not a bearing wall. 

Nonstructural wall. All walls other than bearing walls 
or shear walls. 

Shear wall (vertical diaphragm). A wall, bearing or 
nonbearing, designed to resist lateral seismic forces 
acting in the plane of the wall (sometimes referred to 
as a vertical diaphragm). 

WALL SYSTEM, BEARING. A structural system with 
bearing walls providing support for all or major portions 
of the vertical loads. Shear walls or braced frames provide 
seismic force resistance. 

WIND-RESTRAINT SYSTEM. The collection of struc- 
tural elements that provides restraint of the seismic-isolated 
structure for wind loads. The wind-restraint system may 
be either an integral part of isolator units or a separate 
device. 

9.2.2 Symbols. The unit dimensions used with the items 
covered by the symbols shall be consistent throughout 
except where specifically noted. The symbols and defini- 
tions presented in this Section apply to these provisions 
as indicated. 

A, B, C, D, E, F — the Seismic Performance Categories 
as defined in Tables 9.4.2.1a and 
9.4.2.1b 
A, B, C, D, E t F = the Site Classes as defined in 
Section 9.4.1.2.1 
A ch = cross-sectional area (in. 2 or mm 2 ) of a 

component measured to the outside of the 
special lateral reinforcement 
Ao — the area of the load-carrying foundation 
(ft 2 or m 2 ) 



A vd 
A, 



B D = 



Bm — 



\ sh — total cross-sectional area of hoop 

reinforcement (in. 2 or mm 2 ), including 
supplementary crossties, having a spacing 
of Sh and crossing a section with a core 
dimension of h c 

required area of leg (in. 2 or mm 2 ) of 
diagonal reinforcement 
the torsional amplification factor, 
Section 9.5.5.5.2 

the incremental factor related to P -delta 
effects in Section 9.5.5.7.2 
the amplification factor related to the 
response of a system or component as 
affected by the type of seismic attachment, 
determined in Section 9.6.1.3 
numerical coefficient as set forth in 
Table 9.13.3.3.1 for effective damping 
equal to ftp 

numerical coefficient as set forth in 
Table 9.13.3.3.1 for effective damping 
equal to /? M 
b = the shortest plan dimension of the 
structure, in ft (mm) measured 
perpendicular to d 

C d = the deflection amplification factor as given 
in Table 9.5.2.2 

C s — the seismic response coefficient determined 
in Sections 9.5.5.2.1 and 9.5.9.3.1 
C sm — the modal seismic response coefficient 
determined in Section 9.5.6.5 
(dimensionless) 

Cj = the building period coefficient in 

Section 9.5.3.3 
C vx = the vertical distribution factor as 
determined in Section 9.5.5.4 
c = distance from the neutral axis of a flexural 
member to the fiber of maximum 
compressive strain (in. or mm) 
the effect of dead load 
design displacement, in in. (mm), at the 
center of rigidity of the isolation system in 
the direction under consideration as 
prescribed by Eq. 9.13.3.3,1 

design displacement, in in. (mm), at the 
center of rigidity of the isolation system in 
the direction under consideration, as 
prescribed by Eq. 9.13.4.2-1 

Dm = maximum displacement, in in. (mm), at the 
center of rigidity of the isolation system in 
the direction under consideration, as 
prescribed by Eq. 9.13.3.3.3 

D M f = maximum displacement, in in. (mm), at the 
center of rigidity of the isolation system in 
the direction under consideration, as 
prescribed by Eq. 9.13.4.2-2 



D 

D D 



ZV = 



102 



ASCE 7-02 



D p — relative seismic displacement that the 
component must be designed to 
accommodate as defined in 
Section 9.6.1.4 

D s = the total depth of the stratum in 
Eq. 9.5.9.2.1.2-4 (ft or m) 
D TD — total design displacement, in in. (mm), of 
an element of the isolation system 
including both translational displacement at 
the center of rigidity and the component of 
torsional displacement in the direction 
under consideration as prescribed by 
Eq. 9.13.3.3.5-1 
D TM = total maximum displacement, in in. (mm), 
of an element of the isolation system 
including both translational displacement at 
the center of rigidity and the component of 
torsional displacement in the direction 
under consideration as prescribed by 
Eq. 9.13.3.3.5-2 
d = overall depth of member (in. or mm) in 

Section 9.5 
d = the longest plan dimension of the structure, 
in ft (mm), in Section 9.13 

d p = the longest plan dimension of the structure, 

in ft (mm) 
E = the effect of horizontal and vertical 
earthquake-induced forces, in 
Sections 9.5.2.7 and 9.13 
Ei oop = energy dissipated in kip-in. (kN-mm), in an 
isolator unit during a full cycle of 
reversible load over a test displacement 
range from A + to A ~, as measured by the 
area enclosed by the loop of the 
force-deflection curve 
e — the actual eccentricity, in ft (mm), measured 
in plan between the center of mass of the 
structure above the isolation interface and 
the center of rigidity of the isolation 
system, plus accidental eccentricity, in ft 
(mm), taken as 5% of the maximum 
building dimension perpendicular to the 
direction of force under consideration 

F a = acceleration-based site coefficient 
(at 0.3-sec period) 

F~ = maximum negative force in an isolator unit 
during a single cycle of prototype testing at 
a displacement amplitude of A~ 

F+ = positive force in kips (kN) in an isolator 
unit during a single cycle of prototype 
testing at a displacement amplitude 
of A 4 " 
F/, F n , F x = the portion of the seismic base shear, V, 

induced at Level /, n, or x, respectively, as 
determined in Section 9.5.5.4 



F p = the seismic force acting on a component 

of a structure as determined in Section 

9.6.1.3 
F v — velocity-based site coefficient (at 1.0-sec 

period) 
F x — total force distributed over the height of the 

structure above the isolation interface as 

prescribed by Eq. 9.13.3.5 
F xm = the portion of the seismic base shear, V m , 

induced at Level x as determined in 

Section 9.5.5.6 
f c — specified compressive strength of concrete 

used in design 
f f s — ultimate tensile strength (psi or MPa) of the 

bolt, stud, or insert leg wires. For A307 

bolts or A 108 studs, it is permitted to be 

assumed to be 60,000 psi (415 MPa). 
f y = specified yield strength of reinforcement 

(psi or MPa) 
f v h = specified yield stress of the special lateral 

reinforcement (psi or kPa) 
G — yv^/g = the average shear modulus for the 

soils beneath the foundation at large strain 

levels (psf or Pa) 
Go = yvf /g — the average shear modulus for 

the soils beneath the foundation at small 

strain levels (psf or Pa) 
g = the acceleration due to gravity 
H = thickness of soil 
h — the height of a shear wall measured as the 

maximum clear height from top of 

foundation to bottom of diaphragm framing 

above, or the maximum clear height from 

top of diaphragm to bottom of diaphragm 

framing above 
h = the effective height of the building as 

determined in Section 9.5.9.2 or 9.5.9.3 

(ft or m) 
h c — the core dimension of a component 

measured to the outside of the special 

lateral reinforcement (in. or mm) 
h h h n , h x = the height above the base Level /, n, or jc, 

respectively 
h sx = the story height below Level 

x = (h x — Ajc-i) 
/ = the occupancy importance factor in 

Section 9.1.4 
lo = the static moment of inertia of the 

load-carrying foundation, see 

Section 9.5.9.2.1 (in. 4 or mm 4 ) 
I p = the component importance factor as 

prescribed in Section 9.6.1.5 



Minimum Design Loads for Buildings and Other Structures 



103 



/' = the building level referred to by the 

subscript i; i — 1 designates the first level 
above the base 
K p — the stiffness of the component or 

attachment, Section 9.6.3.3 
K y = the lateral stiffness of the foundation as 
defined in Section 9.5.9.2.1.1 (lb/in. or 
N/m) 
Kq ~ the rocking stiffness of the foundation as 
defined in Section 9.5.9.2.1.1 (ft-lb/degree 
or N-m/rad) 
KL/r — the lateral slenderness of a compression 
member measured in terms of its 
effective buckling length, KL, and the least 
radius of gyration of the member 
cross-section, r 
K Dmax = maximum effective stiffness, in kips/in. 
(kN/mm), of the isolation system at the 
design displacement in the horizontal 
direction under consideration as prescribed 
by Eq. 9.13.9.5.1-1 
Komin = minimum effective stiffness, in kips/in. 
(kN/mm), of the isolation system at the 
design displacement in the horizontal 
direction under consideration as prescribed 
by Eq. 9.13.9.5.1-2 
K max = maximum effective stiffness, in kips/in. 
(kN/mm), of the isolation system at the 
maximum displacement in the horizontal 
direction under consideration as prescribed 
by Eq. 9.13.9.5.1-3 
K m in = minimum effective stiffness, in kips/in. 
(kN/mm), of the isolation system at the 
maximum displacement in the horizontal 
direction under consideration, as prescribed 
by Eq. 9.13.9.5.1-4 
k = the distribution exponent given in 

Section 9.5.5.4 
k = the stiffness of the building as determined 
in Section 9.5.9.2.1.1 (lb/ft or N/m) 
k e ff = effective stiffness of an isolator unit, as 
prescribed by Eq. 9.13.9.3-1 
L = the overall length of the building (ft or m) 
at the base in the direction being analyzed 
L — length of bracing member (in. or mm) in 

Section A.9.8 
L — the effect of live load in Section 9.13 
L = the overall length of the side of the 

foundation in the direction being analyzed, 
Section 9.5.9.2.1.2 (ft or m) 
/ = the dimension of a diaphragm 

perpendicular to the direction of application 
of force. For open-front structures, / is the 
length from the edge of the diaphragm at 
the open-front to the vertical resisting 



elements parallel to the direction of 

the applied force. For a cantilevered 

diaphragm, / is the length of the 

cantilever. 
Mf = the foundation overturning design moment 

as defined in Section 9.5.5.6 

(ft-kip or kN-m) 
M , Mq\ = the overturning moment at the 

foundation- soil interface as determined in 

Sections 9.5.9.2.3 and 9.5.9.3.2 

(ft-lb or N-m) 
M t — the torsional moment resulting from the 

location of the building masses, 

Section 9.5.5.5.2 
M ta = the accidental torsional moment as 

determined in Section 9.5.5.5.2 
M x = the building overturning design 

moment at Level x as defined in 

Section 9.5.5.6 
m = a subscript denoting the mode of vibration 

under consideration; i.e., m — 1 for the 

fundamental mode 
N = number of stories, Section 9.5.5.3.2 
TV = standard penetration resistance, ASTM 
_ D1536-84. 
N = average field standard penetration resistance 

for the top 100 ft (30 m), see 

Section 9.4.1.2.1 
N c h — average standard penetration resistance for 

cohesionless soil layers for the top 100 ft 

(30 m), see Section 9.4.1,2.1 
n = designates the level that is uppermost in the 

main portion of the building 
P D = required axial strength on a column 

resulting from application of dead load, D, 

in Section 9.5 (kip or kN) 
p E — required axial strength on a column 

resulting from application of the amplified 

earthquake load, E\ in Section 9.5 

(kip or kN) 
P L — required axial strength on a column 

resulting from application of live load, L, 

in Section 9.5 (kip or kN) 
P n = nominal axial load strength (lb or N) in 

A.9.8 
P n — the algebraic sum of the shear wall and the 

minimum gravity loads on the joint surface 

acting simultaneously with the shear 

(lb or N) 
P* = required axial strength on a brace (kip or 

kN) in Section A.9.8 
P x = the total unfactored vertical design load at, 

and above, Level x for use in 

Section 9.5.5.7.2 
PI = plasticity index, ASTM D43 18-93. 



104 



ASCE 7-02 



Qe = 
Q v = 

R = 

R P = 

r — 



Si = 

Sds — 
Sd\ — 
Sms = 

Smi = 

S„ = 

■Sft = 

r = 



the effect of horizontal seismic 

(earthquake-induced) forces, Section 9.5.2.7 

the load equivalent to the effect of the 

horizontal and vertical shear strength of the 

vertical segment, Section A. 9. 8 

the response modification coefficient as 

given in Table 9.5.2.2 

the component response modification factor 

as defined in Section 9.6.1.3 

the characteristic length of the foundation 

as defined in Section 9.5.9.2.1 

the characteristic foundation length as 

defined by Eq. 9.5.9.2.1.1-5 (ft or m) 

the characteristic foundation length as 

defined by Eq. 9.5.9.2.1.1-6 (ft or m) 

the ratio of the design story shear resisted 

by the most heavily loaded single element 

in the story, in direction x, to the total story 

shear 

the mapped maximum considered 

earthquake, 5% damped, spectral response 

acceleration at short periods as defined in 

Section 9.4.1.2 

the mapped maximum considered 

earthquake, 5% damped, spectral response 

acceleration at a period of 1 sec as defined 

in Section 9.4.1.2 

the design, 5% damped, spectral response 

acceleration at short periods as defined in 

Section 9.4.1.2 

the design, 5% damped, spectral response 

acceleration at a period of 1 sec as defined 

in Section 9.4.1.2 

the maximum considered earthquake, 5% 

damped, spectral response acceleration at 

short periods adjusted for site class effects 

as defined in Section 9.4.1.2 

the maximum considered earthquake, 5% 

damped, spectral response acceleration at a 

period of 1 sec adjusted for site class 

effects as defined in Section 9.4.1.2 

average undrained shear strength in top 

100 ft (30 m); see Section 9.4.1.2, ASTM 

D2 166-91 or ASTM D2850-87. 

spacing of special lateral reinforcement 

(in. or mm) 

the fundamental period of the building as 

determined in Section 9.5.5.2.1 

the effective fundamental period (sec) of 

the building as determined in 

Sections 9.5.9.2.1.1 and 9.5.9.3.1 

the approximate fundamental period 

of the building as determined in 

Section 9.5.5.3 



T 



T M = 



T D = 



To 
Ts 
Tm 



T D = effective period, in seconds (sec), of the 
seismically isolated structure at the design 
displacement in the direction under 
consideration as prescribed by 
Eq. 9.13.3.3.2 

the modal period of vibration of the m th 
mode of the building as determined in 
Section 9.5.6.5 

effective period, in seconds (sec), of the 
seismically isolated structure at the 
maximum displacement in the direction 
under consideration as prescribed by 
Eq. 9.13.3.3.4 

the fundamental period of the 
component and its attachment, 
Section 9.6.3.3 
0.2S diJ Sds 

Sdi/Sds 

effective period, in seconds (sec), of the 

seismically isolated structure at the 

maximum displacement in the direction 

under consideration as prescribed by 

Eq. 9.13.3.3.4 
74 = net tension in steel cable due to dead load, 

prestress, live load, and seismic load, 

Section A.9.8.8 
V — the total design lateral force or shear at the 

base, Section 9.5.5.2 
Vb — the total lateral seismic design 

force or shear on elements of the 

isolation system or elements below the 

isolation system as prescribed by 

Eq. 9.13.3.4.1 
V s = the total lateral seismic design force 

or shear on elements above the 

isolation system as prescribed by 

Eq. 9.13.3.4.2 
V t = the design value of the seismic base shear 

as determined in Section 9.5.6.8 
V u = required shear strength (lb or N) due to 

factored loads in Section 9.6 
V x — the seismic design shear in story x as 

determined in Section 9.5.5.5 or 9.5.6.8 
V] = the portion of the seismic base shear, V, 

contributed by the fundamental mode, 

Section 9.5.9.3 (kip or kN) 
A V = the reduction in V as determined in 

Section 9.5.9.2 (kip or kN) 
A Vi = the reduction in V\ as determined in 

Section 9.5.9.3 (kip or kN) 
v s = the average shear wave velocity 

for the soils beneath the foundation at 

large strain levels, Section 9.5.9.2 

(ft/s or m/s) 



Minimum Design Loads for Buildings and Other Structures 



105 



v s — average shear wave velocity in top 100 ft 

(30 m), see Section 9.4.1.2 
v so — the average shear wave velocity for the 

soils beneath the foundation at small strain 

levels, Section 9.5.9.2 (ft/s or m/s) 
W — the total gravity load of the building as 

defined in Section 9.5.5.2. For calculation 

of seismic-isolated building period, W is 

the total seismic dead load weight of the 

building as defined in Sections 9.5.9.2 and 
__ 9.5.9.3 (kip or kN). 
W = the effective gravity load of the building as 

defined in Sections 9.5.9.2 and 9.5.9.3 

(kip or kN) 
W c = the gravity load of a component of the 

building 
Wo = the energy dissipated per cycle at the story 

displacement for the design earthquake, 

Section 9.13.3.2 
W m = the effective modal gravity load determined 

in accordance with Eq. 9.5.6.5-2. 
W p — component operating weight (lb or N) 
w = the width of a diaphragm or shear wall in 

the direction of application of force. For 

sheathed diaphragms, the width shall be 

defined as the dimension between the 

outside faces of the tension and 

compression chords. 
w — moisture content (in percent), ASTM 

D2216-92 [3] 
wi, w n , w x = the portion of W that is located at or 

assigned to Level i, n, or x, respectively 
x = the level under consideration 
x = 1 designates the first level above the base 
y — elevations difference between points of 

attachment in Section 9.6 
y = the distance, in ft (mm), between the 

center of rigidity of the isolation system 

rigidity and the element of interest 

measured perpendicular to the direction of 

seismic loading under consideration, 

Section 9.13 
z = the level under consideration; x — 1 

designates the first level above the base 
a — the relative weight density of the structure 

and the soil as determined in 

Section 9.5.9.2.1.1 
a = angle between diagonal reinforcement 

and longitudinal axis of the member 

(degree or rad) 
j3 — ratio of shear demand to shear capacity for 

the story between Level x and x — 1 
J3 — the fraction of critical damping for the 

coupled structure-foundation system, 

determined in Section 9.5.9.2.1 



p D — effective damping of the isolation system at 

the design displacement as prescribed by 

Eq. 9.13.9.5.2-1 
fi M — effective damping of the isolation system at 

the maximum displacement as prescribed 

by Eq. 9.13.5.2-2 
j6 = the foundation damping factor as specified 

in Section 9.5.9.2.1 
p e ff = effective damping of the isolation system as 

prescribed by Eq. 9.13.9.3-2 
y = the average unit weight of soil 

(lb/ft 3 or kg/m 3 ) 
A = the design story drift as determined in 

Section 9.5.5.7.1 
A a = the allowable story drift as specified in 

Section 9.5.2.8 
A m = the design modal story drift determined in 

Section 9.5.6.6 
A + = maximum positive displacement of an 

isolator unit during each cycle of prototype 

testing 
A" = maximum negative displacement of an 

isolator unit during each cycle of prototype 

testing 
8 max = the maximum displacement at Level x, 

considering torsion, Section 9.5.5.5.2 
S avg — the average of the displacements at the 

extreme points of the structure at Level x, 

Section 9.5.5.5.2 
8 X = the deflection of Level x at the center 

of the mass at and above Level x, 

Eq. 9.5.5.7.1 
8 xe — the deflection of Level x at the center 

of the mass at and above Level x 

determined by an elastic analysis, 

Section 9.5.5.7.1 
8 xem = the modal deflection of Level x at the 

center of the mass at and above Level x 

determined by an elastic analysis, 

Section 9.5.6.6 
S xm — the modal deflection of Level x at the 

center of the mass at and above Level x 

as determined by Eqs. 9.5.4.6-3 and 

9.13.3.2-1 
£jc> ^jci = the deflection of Level x at the center of 

the mass at and above Level x, 

Eqs. 9.5.9.2.3-1 and 9.5.9.3.2-1 

(in. or mm) 
= the stability coefficient for P -delta effects 

as determined in Section 9.5.5.7.2 
r = the overturning moment reduction factor, 

Eq. 9.5.3.6 
p = a reliability coefficient based on the extent 

of structural redundance present in a 

building as defined in Section 9.5.2.7 



106 



ASCE 7-02 



p s — spiral reinforcement ratio for precast, 

prestressed piles in Sections A.9.7. 4.4.5 and 
A.9.7.5.4.4 

p x = a reliability coefficient based on the extent 
of structural redundancy present in the 
seismic force-resisting system of a building 
in the x direction 
A. = time effect factor 

(p = the capacity reduction factor 

(j) — the strength reduction factor or resistance 
factor 
(j>i m = the displacement amplitude at the z th level 
of the building for the fixed-base condition 
when vibrating in its m th mode, 
Section 9.5.6.5 
£2o = over strength factor as defined in 
Table 9.5.2.2 
YsEo = total energy dissipated, in kip-ins. 

(kN-mm), in the isolation system during a 
full cycle of response at the design 
displacement, Do 
H£ M = total energy dissipated, in kip-ins. 

(kN-mm), in the isolation system during a 
full cycle of response at the maximum 
displacement, Dm 
^D^\max = sum, for all isolator units, of the 

maximum absolute value of force, in 
kips (kN), at a positive displacement 
equal to D D 
^D + \min = sum, for all isolator units, of the minimum 
absolute value of force, in kips (kN), at a 
positive displacement equal to D D 
7 D~\max = sum > f° r a H isolator units, of the 

maximum absolute value of force, in 
kips (kN), at a negative displacement 
equal to D D 

sum, for all isolator units, of the minimum 
absolute value of force, in kips (kN), at a 
negative displacement equal to D D 
sum, for all isolator units, of the 
maximum absolute value of force, in 
kips (kN), at a positive displacement 
equal to D M 

S|FjVf + | m/ - w = sum, for all isolator units, of the 

minimum absolute value of force, in 
kips (kN), at a positive displacement 
equal to D M 

^\FM~\max = sum, for all isolator units, of the 

maximum absolute value of force, in 
kips (kN), at a negative displacement 
equal to D M 

^\FM~\min = sum > f° r all isolator units, of the 

minimum absolute value of force, in 
kips (kN), at a negative displacement 
equal to D M 



SIFi 



D I min 



M ! max 



SECTION 9.3 

This Section is intentionally left blank. 

9.4.1 Procedures for Determining Maximum Consid- 
ered Earthquake and Design Earthquake Ground 
Motion Accelerations and Response Spectra. Ground 
motion accelerations, represented by response spectra and 
coefficients derived from these spectra, shall be determined 
in accordance with the general procedure of Section 9.4.1.2 
or the site-specific procedure of Section 9.4.1.3. The gen- 
eral procedure in which spectral response acceleration 
parameters for the maximum considered earthquake ground 
motions are derived using Figure 9.4.1.1a through 9.4.1.1J, 
modified by site coefficients to include local site effects 
and scaled to design values, are permitted to be used for 
any structure except as specifically indicated in these pro- 
visions. The site- specific procedure also is permitted to be 
used for any structure and shall be used where specifically 
required by these provisions. 

9.4.1.1 Maximum Considered Earthquake Ground 
Motions. The maximum considered earthquake ground 
motions shall be as represented by the mapped spectral 
response acceleration at short periods, Ss> and at 1-sec, 
Si, obtained from Figure 9.4.1.1a through 9.4/1 . 1 j and 
adjusted for Site Class effects using the site coefficients 
of Section 9.4.1.2.4. When a site-specific procedure is 
used, maximum considered earthquake ground motion 
shall be determined in accordance with Section 9.4.1.3. 

9.4.1.2 General Procedure for Determining Maxi- 
mum Considered Earthquake and Design Spectral 
Response Accelerations. The mapped maximum con- 
sidered earthquake spectral response acceleration at short 
periods (Ss) and at 1-sec (Si) shall be determined from 
Figure 9.4.1.1a through 9.4.1.1J. 

For buildings and structures included in the scope 
of this Standard as specified in Section 9.1.2.1, the 
Site Class shall be determined in accordance with 
Section 9.4.1.2.1. The maximum considered earthquake 
spectral response accelerations adjusted for Site Class 
effects, Sms an d Smi> snal l be determined in accordance 
with Section 9.4.1.2.4 and the design spectral response 
accelerations, Sos and Sou shall be determined in 
accordance with Section 9.4.1.2.5. The general response 
spectrum, when required by these provisions, shall be 
determined in accordance with Section 9.4.1.2.6. 



9.4.1.2.1 Site Class Definitions. The site shall 
classified as one of the following classes: 

A — Hard rock with measured shear wave 
velocity, v s > 5000 ft/s (1500 m/s) 

B = Rock with 2500 ft/s < v s < 5000 ft/s 
(760 m/s < v s < 1500 m/s) 



be 



Minimum Design Loads for Buildings and Other Structures 



107 



TABLE 9.4.1.2 
SITE CLASSIFICATION 



Site Class 


v s 


NorN ch 


s u 


A 
Hard rock 


>5000 ft/s 
(>1500m/s) 


not applicable 


not applicable 


B 
Rock 


2500 to 5000 ft/s 
(760 to 1500 m/s) 


not applicable 


not applicable 


C 

Very dense soil 
and soft rock 


1200 to 2500 ft/s 
(370 to 760 m/s) 


> 50 


> 2000 psf 
(> 100 kPa) 


D 

Stiff soil 


600 to 1200 ft/s 
(180 to 370 m/s) 


15 to 50 


1000 to 2000 psf 
(50 to 100 kPa) 


E 

Soil 


<600 ft/s 
(< 180 m/s) 


<15 


< 1000 psf 
(<50 kPa) 


Any profile with more than 10 ft of soil having the following characteristics: 

— Plasticity index PI > 20, 

— Moisture content w > 40%, and 

— Undrained shear strength s u < 500 psf 


F Soils requiring site-specific 
evaluation 


1. Soils vulnerable to potential failure or 
collapse 

2. Peats and/or highly organic clays 

3. Very high plasticity clays 

4. Very thick soft/medium clays 



C = Very dense soil and soft rock with 1200 ft/s < 
Vs_ < 2500 ft/s (370 m/s < v s < 760 m/s) or 
77 or N ch > 50 or s u > 2000 psf (100 kPa) 

D = Stiff soil with 600 ft/s < v s < 1200 ft/s _ 
(180 m/s < v s < 370 m/s) or with 15 < N 
or N ch < 50 or 1000 psf < s u < 2000 psf 
(50 kPa < s u < 100 kPa) 

E = A soil profile with v s < 600 ft/s (180 m/s) or 
any profile with more than 10 ft (3 m) of soft 
clay. Soft clay is defined as soil with PI > 20, 
w > 40%, and s u < 500 psf (25 kPa) 

F — Soils requiring site-specific evaluations: 

1. Soils vulnerable to potential failure or collapse 
under seismic loading such as liquefiable soils, 
quick and highly sensitive clays, collapsible 
weakly cemented soils. 

Exception: For structures having fundamen- 
tal periods of vibration equal to or less 
than 0.5-sec, site-specific evaluations are 
not required to determine spectral accel- 
erations for liquefiable soils. Rather, the 
Site Class may be determined in accordance 
with Section 9.4.1.2.2 and the corresponding 
values of F a and F v determined from 
Tables 9.4.1.2.4a and 9.4.1.2.4b. 

2. Peats and/or highly organic clays (H > 10 ft 
[3 m] of peat and/or highly organic clay where 
H — thickness of soil). 



3. Very high plasticity clays (H > 25 ft [7.6 m] 
with PI > 75). 

4. Very thick soft/medium stiff clays (H > 120 ft 
[37 m]). 

Exception: When the soil properties are not 
known in sufficient detail to determine the 
Site Class, Class D shall be used. Site Class E 
shall be used when the authority having 
jurisdiction determines that Site Class E is 
present at the site or in the event that Site 
E is established by geo technical data. 

The following standards are referenced in the 
provisions for determining the seismic coefficients: 

[1] ASTM. "Test Method for Penetration Test and 
Split-Barrel Sampling of Soils." ASTM DI586- 
84, 1984. 

[2] ASTM. "Test Method for Liquid Limit, Plastic 
Limit, and Plasticity Index of Soils." ASTM 
D43I8-93, 1993. 

[3] ASTM. "Test Method for Laboratory Determi- 
nation of Water (Moisture) Content of Soil and 
Rock." ASTM D22I6-92, 1992. 

[4] ASTM. "Test Method for Unconfined Compres- 
sive Strength of Cohesive Soil." ASTM D2I66- 
91, 1991. 

[5] ASTM. "Test Method for Unconsolidated, Un- 
drained Compressive Strength of Cohesive Soils 
in Triaxial Compression." ASTM D2850-87, 
1987. 



108 



ASCE 7-02 



This page intentionally left blank. 



Minimum Design Loads for Buildings and Other Structures 109 




FIGURE 9.4.1.1(a) 

MAXIMUM CONSIDERED EARTHQUAKE GROUND MOTION FOR 

CONTERMINOUS UNITED STATES. OF 0.2 s SPECTRAL RESPONSE 

ACCELERATION (5% OF CRITICAL DAMPING), SITE CLASS B 



110 



ASCE 7-02 




Areas with a constant spectral 
response acceleration of 1 50% g 



Point valus of spectral response 
acceleration expressed as a percent 
uf gravity 



Contours of spectral response 
acceleration expressed as a percent 
of gravity. Hachures point in 
direction of decreasing values. 



Scale 1:13,000,000 
100 200 300 400 



100 100 200 300 400 500 600 KILOMETERS 



FIGURE 9.4.1.1(a) - continued 

MAXIMUM CONSIDERED EARTHQUAKE GROUND MOTION FOR 

CONTERMINOUS UNITED STATES. OF 0.2 s SPECTRAL RESPONSE 

ACCELERATION (5% OF CRITICAL DAMPING), SITE CLASS B 



Minimum Design Loads for Buildings and Other Structures 



111 




The acceleration values contoured are the random 
horizontal component For design purposes, the 
reference site condition for the map is to be taken as 
NEHRP site class B, 

Regional maps should be used when additional detail 
is required 



Building Seismic Safety Council, 1 993, NEHRP 
Recommended Provisions for Seismic Regulations 
for New Buildings and other Structures, FEMA 303. 

Frankel, A, Mueller, C, Bamhard, T., Parkins, D., 
Leyendecker, EV., Dtckman, K, Hareon, S., and 
Hopper, M, 1 996, National Seismic- Hazard Maps: 
Documentation June 1 996: US. Geological Survev 
Open-File Report 96-532, 11 Op. 

Frankel, A., Mueller, C, Barnhard, T., Perkins, D., 
Leyendecker, EV., DJckman, K, Hanson, S., and 
Hopper, M., 1 997, Seismic - Hazard Maps for the 
Contermime United States, Map L • Horizontal 
Spectral Response Acceleration for 1 .0 Second 
Period with 2% Probability of Exceedance in 50 
Years: U.S. Geological Survey Open-File Report 
97-131-L,scalel:7,000.0(X). 

Peteisen, M, Bryaivt, W., Cramer, C, Cao, T., 
Reichle, M, Frankel, A, Lienkaemper, X, 
McCrory, P., and Schwartz, D., 19%, Probabilistic 
Seismic Hazard Assessment for the State of 
California: California Division of Mines and 
Geology Open-File Report 96-08, 66 pi, and U.S. 
Geological Survey Open-File Report 96-706, 66 p 

Map prepared by US. Geological Survey, 



Index of detailed regional maps at larger scales 



FIGURE 9.4.1.1(b) 

MAXIMUM CONSIDERED EARTHQUAKE GROUND MOTION FOR 

CONTERMINOUS UNITED STATES OF 1.0 s SPECTRAL RESPONSE 

ACCELERATION (5% OF CRITICAL DAMPING), SITE CLASS B 



112 



ASCE 7-02 




600 KILOMET1ERS 



FIGURE 9.4.1.1(b) - continued 

MAXIMUM CONSIDERED EARTHQUAKE GROUND MOTION FOR 

CONTERMINOUS UNITED STATES OF 1.0s SPECTRAL RESPONSE 

ACCELERATION (5% OF CRITICAL DAMPING), SITE CLASS B 



Minimum Design Loads for Buildings and Other Structures 



113 




114 



ASCE 7-02 



§ 

5 

3 
c 

3 

o 

& 
w . 
<5' 

D 

I- 

O 

Q> 

a 



CO 



3 
(Q 
(ft 
fU 
3 
Q. 

o 

3" 

» 

C 

o 






MM 



Cuatuur intervals, * g 



Note, cootuuaaieinegularty spaced 



E_ 



Aff-ii wilh a LUtoiUn) special 
[tsifUHtw^cclcntiiiD of 1S0% g 



Point value of spectral rtspiitec 
of gravity 



Conltimv of spectral icspuust: 
acceleration expressed as a ivfuent 
of gravity. Huchurcs point in 
diieciii wi 1 4 tk^ftaaiiig valuei. 



Locations of faults (see DISCUSSION). 
The auntber on the fault is the 
median spectral (espnnse atculeratiiHi 
limes I 5. expressed as a peiceul of 
gravity. 



DISCUSSION 

The acceleration values conkmnsi are the raadoro honaoalal 
component, ft* dsMjJD poroses, the reference sins uuoditiim Is* 
the map ii to he titan as NEHRP site class B. 

A line thown as a hull location is the pnijection to the earth' s 
surface of the wl^ of the fault rupture a/ea located closest hi 
the earth's surface. Only the portton oil the fault used in 
determUiingkJtsign values is ihtmu The uumberuAtius fault is the 
detcrauAUtk median spectral response acceleration times 15 The 
values oo the fault gxHtiiHi shown may he ubed hu interpolation 

Selected contours Bear faults have been deleted for cfcuity In 
the** u&tutta, iiucipolauou nay be done using fault valuta, and the 
neai&i adjacent contour 




200 KILOMETERS 



FIGURE 9.4.1.1(c) 

MAXIMUM CONSIDERED EARTHQUAKE GROUND MOTION FOR REGION 1 OF 0.2 s SPECTRAL RESPONSE 

ACCELERATION (5% OF CRITICAL DAMPING), SITE CLASS B 




116 



ASCE 7-02 



3 

G 

3 
D 

<D 
(0 
<5" 

3 

r* 

o 

Q) 
Q. 
« 



09 

c 



3 
« 

a 






.i^^iXl£IM\^K 



Expls 

Contour intervals, % g 



Note: contours are irregularly spaced 



^1 Areas with a constant spectral 

-^ response acceleration of 60% g 



JH^int value of spectral response 
acceleration expressed as a percent 
of gravity 



Contours of spectral response 
acceleration expressed as a percent 
of gravity. Hachures point in 
direction of decreasing values. 



24S Locations of faults (see DISCUSS ION). 

The number on the fault is the 
median spectral response acceleration 
times 1 .5, expressed as a percent of 
gravity. 



DISCUSSION 

The acceleration values contoured are the random horizontal 
component rur design purposes, the reference site condition for 
the map is to be taken as NEHRPsits class B. 

A line shown as a fault location is the projection to the earth's 
surface of the edge of the fault rupture area located closest to 
the earth's surface. Only the portion of the fault used in 
determining design values is shown. The number on the fault is the 
deterministic median spectral response acceleration times 1 .5. The 
values on the fault portion shown may be used for interpolation 

Selected contours near faults ha ve been deleted for clarity. In 
these instances, interpolation may be done using fault values and the 
nearest adjacent contour. 




200 KILOMETERS 



FIGURE 9.4.1.1(d) 

MAXIMUM CONSIDERED EARTHQUAKE GROUND MOTION FOR REGION 1 OF 1.0 s SPECTRAL RESPONSE 

ACCELERATION (5% OF CRITICAL DAMPING), SITE CLASS B 



o 
m 






Explanation 


Contour intervals, % g 


200 




175 




nso 




125 




100 

90 




60 




20 




5 









Note: contours are irregularly spaced 


+ 
6.2 


Fuint value of spectral response 
acceleration expressed as a percent 
ofgravity 




Contours of spectral response 
acceleration expressed as a percent 
of gravity. Hachures point in 
direction of decreasing values. 




DISCUSSION 


The acceleration values contoured are the random horizontal 
component Rjr design purposes, (he reference site condition for 
the map is to be taken as NEHRP site class B, 



s 



3 

c 
3 
o 

w 

r- 

o 

01 

a 



S3 



3 

CO 
BJ 
3 

a 



3° 




Scale 1:3.500,000 




Index map showing location of study ai 



- J- I I— =T 



100 KILOMETERS 



FIGURE 9.4.1.1(e) 

MAXIMUM CONSIDERED EARTHQUAKE GROUND MOTION FOR REGION 2 OF 0.2 s SPECTRAL RESPONSE 

ACCELERATION {5% OF CRITICAL DAMPING), SITE CLASS B 




Contour intervals, % g 



Note; cmtfours are irregularly spaced 



R)inl value of spectral response 
acceleration expressed as a peiceffi 
of gravity 



Contains of spectral response 
acceleration expressed as a percent 
of gravity. Hachures point in 
direction of decreasing values. 



The acceleration values contoured are the random horizontal 
component R>r design puiposes, the reference site condition foi 
the map is to be taken as NEHRP site class B. 



> 

V) 

o 

m 



© 



3 

c 
3 

D 

(!) 
(/) 

<5" 

3 

r- 
o 

Q) 

a 

(0 



03 

E. 
a 
5' 

w 
A) 

3 

a 

O 

p+ 

3" 
(D 

C 

o 





Scale 1:3,500,000 



Index map showing location of study area 



100 KSLOMETCRS 



FIGURE 9.4.1.1(f) 

MAXIMUM CONSIDERED EARTHQUAKE GROUND MOTION FOR REGION 2 OF 1.0 s SPECTRAL RESPONSE 

ACCELERATION (5% OF CRITICAL DAMPING), SITE CLASS B 




Scale 1:17,000,000 



750 KILOMETERS 



> 

0) 

o 

m 



FIGURE 9.4.1.1(g) 

MAXIMUM CONSIDERED EARTHQUAKE GROUND MOTION FOR ALASKA OF 0.2 s SPECTRAL RESPONSE 

ACCELERATION (5% OF CRITICAL DAMPING), SITE CLASS B 



5 

3 
c 

3 

(D 
(A 
t5" 

3 

P- 

o 

0) 
Q. 
CO 



CO 

E. 

a 
5" 

CD 
W 

a> 

3 

a 



3- 

o 
•°% 

eg 

-^ 
c 
o 

3 




Scale 1.17,000,000 



750 KILOMETERS 



FIGURE 9.4.1 .1 (g) - continued 

MAXIMUM CONSIDERED EARTHQUAKE GROUND MOTION FOR ALASKA OF 1.0 s SPECTRAL RESPONSE 

ACCELERATION (5% OF CRITICAL DAMPING), SITE CLASS B 




Contour intervals, % g 



CD 



Note: contours are irregularly spaced 



with a constant spectral 
response acceleration of 1 50% g 



Point val ue of spectral response 
acceleration expressed as a percent 
of gravity 



Contours of spectral response 
acceleration expressed as a percent 
of gravity, Hachures point in 
direction of decreasing values. 



Locations of deterministic zone 
boundaries (see DISCUSSION* 
The number on the boundary and 
inside the zone is the median 
spectral response acceleration 
times L5, expressed as a 
percent of gravity. 

DISCUSSION 

The acceleration values contoured are the random horizontal 
component fi>r design purposes, the reference site condition 
for the map is to be taken as NEHRPsile class B. 

The two areas shown as zone boundaries are the projection to 
the earth' s surface of horizontal rupture planes at 9 km depth. 
Spectral accelerations are constant within the boundaries of the 
zones. The number on the boundary and inside the zone is the 
median spectral response acceleration times 1 .5. 

REFERENCES 

Building Seismic Safety Council, 1 998, NEHRP 
Recommended Provisions for Seismic Regulations 
for New Buildings and other Structures, FEMA 302. 

US. Geological Survey National Seismic - Hazard Mapping Project, 
1 998, Hawaii Seismic-Hazard Maps: Documentation: U.S. 
Geological Survey Open-Hie Report, in progress. 

U.S. Geological Survey National Seismic - Hazard Mapping Project, 
J 993, Seismic - Hazard Maps of Hawaii: US. Geological Survey 
Opcn-Rlc Report, 6 sheets, scale 1 : 2,000,000, in progress. 

Map prepared by US. Geological Survey. 




Scale 1:3,500,000 



1SO KILOMETERS 



> 

w 
o 
m 

-a 

■ 

o 

to 



FIGURE 9.4.1.1(h) 

MAXIMUM CONSIDERED EARTHQUAKE GROUND MOTION FOR HAWAII OF 0.2 s SPECTRAL RESPONSE 

ACCELERATION (5% OF CRITICAL DAMPING), SITE CLASS B 



i 

5' 
3" 



o 



o 
a 



us 



3 
CO 
W 

0) 

3 

a 



3" 




150 KILOMETERS 



FIGURE 9.4.1.1(h) - continued 

MAXIMUM CONSIDERED EARTHQUAKE GROUND MOTION FOR HAWAII OF 1.0 s SPECTRAL RESPONSE 

ACCELERATION (5% OF CRITICAL DAMPING), SITE CLASS B 



cn 






puERTOiaeo 

(UNITEP STATES] 



100% g 






/ 
/ 
/ 
/ 

/ 
/ 



7 



> STATES 



IStJ\ DE VIEQUES 
(UNITED STATES) 



150% g 



KTOU 



i£g 



i^miED KINGDOM) 



> \w 






THOMAS 

SD STATES) ■:■.■$ 



D STATES) 






^r^-;. 



REFERENCES 

Building Seismic Safety Council, 1 998, NEHRP 
Recommended Provisions for Seismic Regulations 
for New Buildings and other Structures. FEMA 302 

Map prepared by US Geological Survey. 



/ 
/ 

/ 






SAINT CROIX 
(UNITED STATES) , 



0,2 SEC SPECTRAL RESPONSE ACCELERATION (5% OF CRITICAL DAMPING) 



PUERTO RICO 
(UNITED STATES) 









/ 



S 






TORTOhA 






40% g 



■m 



— 7 

/ 
/ 
/ 



M 



iCULEBRA 
D STATES) 

' v - ' " SAINT Tl*li 



(UNnm» KINGDOM) ; 






VIES) 



—, 



ISLA DE VIEQUES 
(UNITED STATES) 



^-•'"c-^. .-•""" 



REFERENCES 

Building Seismic Safety Council, 1 998, NEHRP 
Recommended Provisions for Seismic Regulations 
for New Buildings and other Structures, FEMA 302 

Map prepared by US. Geological Survey. 



SAINT CROIX 
(UNITED STATES), 



1.0 SEC SPECTRAL RESPONSE ACCELERATION (5% OF CRITICAL DAMPING) 



Scale 1:2000,000 



25 50 



100 KILOMETERS 



FIGURE 9.4.1.1(1) 

MAXIMUM CONSIDERED EARTHQUAKE GROUMD MOTION FOR PUERTO 

RICO, CULEBRA, VIEQUES, ST. THOMAS, ST. JOHN, AND ST. CROIX OF 0.2 

AND 1.0 s SPECTRAL RESPONSE ACCELERATION (5% OF CRITICAL 

DAMPING), SITE CLASS B 



126 



ASCE 7-02 



150% g 


: : : .7/ /'.■", ;'•': 


1 




GUAM 
(UNTIED STATES) 


W-B-Wg^xV 



REFERENCES 

Building Seismic Safety Council, 1 998, NEHRP 
Recommended Provisions for Seismic Regulations 
for New Buildings and other Structures, FEMA 301 

Map prepared by U.S. Geological Survey. 



O 



TUTUILA 
(UNTIED STATES) 



0.2 SEC SPECTRAL RESPONSE ACCELERATION (5% OF CRITICAL DAMPING) 



60% g 



m 



YX> : ='}?-;^ 



GUAM 
(UNITED STATES) 



_A~ 



/•\jnS-;-; 



13°00'N 



REFERENCES 

Building Seismic Safety Council, 1 998, NEHRP 
Recommended Provisions for Seismic Regulations 
for New Buildings and other Structures, FEMA 30Z 

Map prepared by US. Geological Survey. 



14*30' 



40% g 


!!®Sf! 


KSIBS? 


(UNITED STATES) 



144°45 r HS'OffE 171°00' K 

1.0 SEC SPECTRAL RESPONSE ACCELERATION (5% OF CRITICAL DAMPING) 



Scale 1:1,000,000 




25 KILOMETERS 



FIGURE 9.4.1.1(j) 

MAXIMUM CONSIDERED EARTHQUAKE GROUND MOTION FOR GUAM 

AND TUTUILLA OF 0.2 AND 1.0 S SPECTRAL RESPONSE ACCELERATION 

(5% OF CRITICAL DAMPING), SITE CLASS B 



Minimum Design Loads for Buildings and Other Structures 



127 



9.4.1.2.2 Steps for Classifying a Site. The Site 
Class of a site shall be determined using the follow- 
ing steps: 

Step 1: Check for the four categories of Site Class F 
requiring site- specific evaluation. If the site 
corresponds to any of these categories, clas- 
sify the site as Site Class F and conduct a 
site-specific evaluation. 

Step 2: Check for the existence of a total thickness 
of soft clay > 10 ft (3 m) where a soft clay 
layer is defined by s u < 500 psf (25 kPa), 
w > 40%, and PI > 20. If this criterion is 
satisfied, classify the site as Site Class E. 

Step 3: Categorize the site using_one of the following 
three methods with v Si N, and s u computed 
in all cases as specified by the definitions in 
Section 9.4.1.2.3. 

a. The v s method: Determine v s for the top 
100 ft (30 m) of soil. Compare the value 
of v s with those given in Section 9.4.1.2 
and Table 9.4.1.2 and assign the corre- 
sponding Site Class. 

v s for rock, Site Class B, shall be 
measured on-site or estimated by a 
geotechnical engineer or engineering 
geologist/seismologist for competent rock 
with moderate fracturing and weathering. 
v s for softer and more highly fractured 
and weathered rock shall be measured on- 
site or shall be classified as Site Class C. 
The classification of hard rock, Site 
Class A, shall be supported by on-site 
measurements of v s or on profiles of the 
same rock type in the same formation with 
an equal or greater degree of weathering 
and fracturing. Where hard rock condi- 
tions are known to be continuous to a 
depth of at least 100 ft (30 m), surficial 
measurements of v s are not prohibited 
from being extrapolated to assess v s . 
The rock categories, Site Classes A and 
B, shall not be assigned to a site if there 
is more than 10 ft (3 m) of soil between 
the rock surface and the bottom of the 
spread footing or mat foundation. 

b. The N method: Determine N for the top 
100 ft (30 m) of soil. Compare the value 
of TV with those given in Section 9.4.1.2 
and Table 9.4.1.2 and assign the corre- 
sponding Site Class. 

c. The J u method: For cohesive soil layers, 
determine s u for the top 100 ft (30 m) of 
soil. For cohesionless soil layers, deter- 
mine N ch for the top 100 ft (30 m) of soil. 



Cohesionless soil is defined by a PI < 
20 where cohesive soil is defined by a 
PI > 20. Compare the values of s u and 
N c h with those given in Section 9.4.1.2 
and Table 9.4.1.2 and assign the corre- 
sponding Site Class. When the N ch and 
~s u criteria differ, assign the category with 
the softer soil (Site Class E soil is softer 
than D). 

9.4.1.2.3 Definitions of Site Class Parameters. The 

definitions presented below apply to the upper 1 00 ft 
(30 m) of the site profile. Profiles containing distinctly 
different soil layers shall be subdivided into those 
layers designated by a number that ranges from 1 
to n at the bottom where there are a total of n distinct 
layers in the upper 100 ft (30 m). Where some of 
the n layers are cohesive and others are not, k is the 
number of cohesive layers and m is the number of 
cohesionless layers. The symbol / refers to any one 
of the layers between 1 and n. 

v S i is the shear wave velocity in ft/s (m/s). 

di is the thickness of any layer between and 
100 ft (30 m). 



v, is 



v x = 



v-a dj_ 



(Eq. 9.4.1.2-1) 



whereby Y^d; is equal to 100 ft (30 m) 



i=l 



N[ is the standard penetration resistance, ASTM 
D1586-84 not to exceed 100 blows/ft as directly 
measured in the field without corrections. 



N is: 



AT 



1=1 

n A 

Y^ zL 



(Eq. 9.4.1.2-2) 



N ch is: 



N ch = 



EzL 
N; 



(Eq. 9.4.1.2-3) 



i=i 



whereby Y^d; =d s . (Use only d ( and N t for 

cohesionless soils.) 

d s is the total thickness of cohesionless soil layers 
in the top 100 ft (30 m) 



128 



ASCE 7-02 



s U i is the undrained shear strength in psf (kPa), not 
to exceed 5000 psf (240 kPa), ASTM D2 166-91 
or D2850-87. 



s u is 



s u = 



d c 






(Eq. 9.41.2-4) 



k 

E< 

= 1 



whereby 2_ d- t = d ( 



d c is the total thickness (100 — d s ) of cohesive soil 
layers in the top 100 ft (30 m) 

PI is the plasticity index, ASTM D43 18-93 

w is the moisture content in percent, ASTM 
D22 16-92 

9.4.1.2.4 Site Coefficients and Adjusted Maximum 
Considered Earthquake Spectral Response Accel- 
eration Parameters. The maximum considered earth- 
quake spectral response acceleration for short periods 
(Sms) and at 1-sec (Sm\), adjusted for site class 
effects, shall be determined by Eqs. 9.4.1.2.4-1 and 
9.4.1.2.4-2, respectively. 



Sms = FaSs 

Sm\ = F V S\ 



(Eq. 9.4.1.2.4-1) 
(Eq. 9.4.1.2.4-2) 



where 



the mapped maximum considered earthquake 
spectral response acceleration at a period of 
1-sec as determined in accordance with 
Section 9.4.1 



Ss = the mapped maximum considered earthquake 
spectral response acceleration at short periods 
as determined in accordance with Section 9.4.1 

where site coefficients F a and F v are defined in 
Tables 9.4.1.2.4a and b, respectively. 



9.4.1.2.5 Design Spectral Response Acceleration 
Parameters. Design earthquake spectral response 
acceleration at short periods, S^s, and at 1-sec period, 
S D u shall be determined from Eqs. 9.4.1.2.5-1 and 
9 .4.1. .2.5-2, respectively. 



Sds = ~Sms 



Sd\ — T^Ml 



(Eq. 9.4.1.2.5-1) 
(Eq. 9.4.1.2.5-2) 



9.4.1.2.6 General Procedure Response Spectrum. 
Where a design response spectrum is required by 
these provisions and site-specific procedures are 
not used, the design response spectrum curve shall 
be developed as indicated in Figure 9.4.1.2.6 and 
as follows: 

1. For periods less than or equal to 7b, the 
design spectral response acceleration, S a , shall 
be taken as given by Eq. 9.4.1.2.6-1: 



S a = S DS 0.4 + 0.6 



7b, 
(Eq. 9.4.1.2.6-1) 



TABLE 9.4.1.2.4a 

VALUES OF F a AS A FUNCTION OF SITE CLASS AND MAPPED SHORT PERIOD MAXIMUM 

CONSIDERED EARTHQUAKE SPECTRAL ACCELERATION 



Site Class 


Mapped Maximum Considered Earthquake 
Spectral Response Acceleration at Short Periods 


S s < 0.25 


S s = 0.5 


S$ = 0.75 


S s = 1.0 


S s > 1.25 


A 


0.8 


0.8 


0.8 


0.8 


0.8 


B 


1.0 


1.0 


1.0 


1.0 


l.O 


C 


1.2 


1.2 


1.1 


1.0 


1.0 


D 


1.6 


1.4 


1.2 


1.1 


1.0 


E 


2.5 


1.7 


1.2 


0.9 


0.9 


F 


a 


a 


a 


a 


a 



Note: Use straight-line interpolation for intermediate values of Ss- 

a Site-specific geotechnical investigation and dynamic site response analyses shall be performed except that for structures 
with periods of vibration equal to or less than 0.5-seconds, values of F a for liquefiable soils may be assumed equal to the 
values for the site class determined without regard to liquefaction in Step 3 of Section 9.4.1.2.2. 



Minimum Design Loads for Buildings and Other Structures 



129 



TABLE 9.4.1.2.4b 

VALUES OF F v AS A FUNCTION OF SITE CLASS AND MAPPED 

1 -SECOND PERSOD MAXIMUM CONSIDERED EARTHQUAKE 

SPECTRAL ACCELERATION 



Site Class 


Mapped Maximum Considered Earthquake 
Spectral Response Acceleration at 1 -Second Periods 


Si < 0.1 


Si = 0.2 


S-, = 0.3 


Si = 0.4 


Si > 0.5 


A 


0.8 


0.8 


0.8 


0.8 


0.8 


B 


1.0 


1.0 


1.0 


1.0 


1.0 


C 


1.7 


1.6 


1.5 


1.4 


1.3 


D 


2.4 


2.0 


1.8 


1.6 


1.5 


E 


3.5 


3.2 


2.8 


2.4 


2,4 


F 


a 


a 


a 


a 


a 



Note; Use straight-line interpolation for intermediate values of S\ . 

a Site-specific geotechnical investigation and dynamic site response analyses shall be 
performed except that for structures with periods of vibration equal to or less than 0.5- 
seconds, values of F v for liquefiable soils may be assumed equal to the values for the site 
class determined without regard to liquefaction in Step 3 of Section 9.4.1.2.2. 




FIGURE 9.4.1.2.6 
DESIGN RESPONSE SPECTRUM 



2. For periods greater than or equal to To and less 
than or equal to T s , the design spectral response 
acceleration, S a , shall be taken as equal to Sos- 

3. For periods greater than T$, the design spectral 
response acceleration, S a , shall be taken as 
given by Eq. 9.4.1.2.6-2: 



S a = 



Sd\ 



(Eq. 9.4.1.2.6-2) 



where 



Sos = the design spectral response accelera- 
tion at short periods 

S D \ = the design spectral response accelera- 
tion at 1-sec period, in units of g-sec 



T = the fundamental period of the structure 

(sec) 
T = 02S Dl /S DS and 
Ts — Sdi/Sds- 

9.4.1.3 Site-Specific Procedure for Determining 
Ground Motion Accelerations, A site- specific study 
shall account for the regional seismicity and geology, 
the expected recurrence rates and maximum magnitudes 
of events on known faults and source zones, the location 
of the site with respect to these near source effects, if 
any, and the characteristics of subsurface site conditions. 

9.4.1.3.1 Probabilistic Maximum Considered 
Earthquake. When site- specific procedures are uti- 
lized, the maximum considered earthquake ground 
motion shall be taken as that motion represented by 
a 5% damped acceleration response spectrum hav- 
ing a 2% probability of exceedance within a 50-year 
period. The maximum considered earthquake spectral 
response acceleration at any period S ci m shall be taken 
from that spectrum. 

Exception: Where the spectral response ordinates 
or a 5% damped spectrum having a 2% probability 
of exceedance within a 50-year period at periods of 
1.0- or 0.2-sec exceed the corresponding ordinate 
of the deterministic limit of Section 9.4.1.3.2, the 
maximum considered earthquake ground motion 
shall be taken as the lesser of the probabilistic 
maximum considered earthquake ground motion or 
the deterministic maximum considered earthquake 
ground motion of Section 9.4.1.3.3 but shall not 



130 



ASCE 7-02 



1.5 F a 



0.6 FJT 




Period T (sec.) 



it shall not be taken as less than 90% of the peak 
spectral acceleration, S a , at any period. The parameter 
Soi shall be taken as the greater of the spectral 
acceleration, S a , at a period of 1 sec or two times 
the spectral acceleration, S a , at a period of 2 sec. The 
parameters Sms and 5m i shall be taken as 1.5 times 
Sds and 5/)i, respectively. 

9.4.2 Seismic Design Category. Structures shall be 
assigned a Seismic Design Category in accordance with 
Section 9.4.2.1. 



FIGURE 9.4.1.3.2 

DETERMINISTIC LIMIT ON MAXIMUM CONSIDERED 

EARTHQUAKE RESPONSE SPECTRUM 

be taken less than the deterministic limit ground 
motion of Section 9.4.1.3.2. 

9.4.1.3.2 Deterministic Limit on Maximum Con- 
sidered Earthquake Ground Motion. The deter- 
ministic limit on maximum considered earthquake 
ground motion shall be taken as the response spec- 
trum determined in accordance with Figure 9.4.1.3.2, 
where F a and F v are determined in accordance with 
Section 9.4.1.2.4, with the value of S s taken as 1.5 g 
and the value of Si taken as 0.6 g. 



9.4.1.3.3 Deterministic Maximum Considered 

Earthquake Ground Motion. The deterministic 
maximum considered earthquake ground motion 
response spectrum shall be calculated as 150% of the 
median spectral response accelerations (S u m) at all 
periods resulting from a characteristic earthquake on 
any known active fault within the region. 

9.4.1.3.4 Site-Specific Design Ground Motion. 
Where site-specific procedures are used to determine 
the maximum considered earthquake ground motion 
response spectrum, the design spectral response 
acceleration at any period shall be determined from 
Eq. 9.4.1.3.4: 



^a — - &aM 



(Eq. 9.4.1.3.4) 



and shall be greater than or equal to 80% of the 
S a determined by the general response spectrum in 
Section 9.4.1.2,6. 

9.4.1.3.5 Design Acceleration Parameters. Where 
the site-specific procedure is used to determine 
the design ground motion in accordance with 
Section 9.4.1.3.4, the parameter S DS shall be taken 
as the spectral acceleration, S a , obtained from the 
site-specific spectra at a period of 0.2 sec, except that 



9.4.2.1 Determination of Seismic Design Category. 
All structures shall be assigned to a Seismic Design Cat- 
egory based on their Seismic Use Group and the design 
spectral response acceleration coefficients, Sos and Sp\, 
determined in accordance with Section 9.4.1.2.5. Each 
building and structure shall be assigned to the most 
severe Seismic Design Category in accordance with 
Table 9.4.2.1a or 9.4.2.1b, irrespective of the fundamen- 
tal period of vibration of the structure, T. 

9.4.2.2 Site Limitation for Seismic Design Cate- 
gories E and F. A structure assigned to Category E or 
F shall not be sited where there is a known potential for 
an active fault to cause rupture of the ground surface at 
the structure. 

Exception: Detached one- and two- family dwellings 
of light-frame construction. 

9.4.3 Quality Assurance. The performance required of 
structures in Seismic Design Categories C, D, E, or F 
requires that special attention be paid to quality assur- 
ance during construction. Refer to A. 9. 3 for supplemen- 
tary provisions. 

TABLE 9.4.2.1 a 

SEISMIC DESIGN CATEGORY BASED ON SHORT 

PERIOD RESPONSE ACCELERATIONS 



Value of S D s 


Seismic Use Group 


I 


li 


ill 


S ds <0.167g 


A 


A 


A 


0.167g < S DS < 0.33g 


B 


B 


C 


0.33g < S os < 0.50g 


C 


C 


D 


0.50g < Sox 


D a 


D a 


D a 



a Seismic Use Group I and II structures located on sites with mapped max- 
imum considered earthquake spectral response acceleration at 1 -second 
period, Si, equal to or greater than 0.75g shall be assigned to Seismic 
Design Category E and Seismic Use Group III structures located on such 
sites shall be assigned to Seismic Design Category F. 



Minimum Design Loads for Buildings and Other Structures 



131 



TABLE 9.4.2.1 b 

SEISMIC DESIGN CATEGORY BASED ON 

1 -SECOND PERIOD RESPONSE ACCELERATIONS 



Value of S i 


Seismic Use Group 


I 


it 


ill 


S Dl < 0.067g 


A 


A 


A 


0.067g<S D i <0.133g 


B 


B 


C 


0.133g < Soi < 0.20g 


C 


C 


D 


0.20g < S Dl 


D a 


D a 


D a 



a Seismic Use Group I and II structures located on sites with mapped max- 
imum considered earthquake spectral response acceleration at 1 -second 
period, Si, equal to or greater than 0.75g shall be assigned to Seismic 
Design Category E and Seismic Use Group III structures located on such 
sites shall be assigned to Seismic Design Category F. 



limits when the structure is subjected to the design seis- 
mic forces. 

A continuous load path, or paths, with adequate 
strength and stiffness shall be provided to transfer all 
forces from the point of application to the final point 
of resistance. The foundation shall be designed to resist 
the forces developed and accommodate the movements 
imparted to the structure by the design ground motions. 
The dynamic nature of the forces, the expected ground 
motion, and the design basis for strength and energy 
dissipation capacity of the structure shall be included in 
the determination of the foundation design criteria. 

Allowable Stress Design is permitted to be used to 
evaluate sliding, overturning, and soil bearing at the soil- 
structure interface regardless of the design approach used 
in the design of the structure. 



SECTION 9.5 
STRUCTURAL DESIGN CRITERIA, ANALYSIS, 

AND PROCEDURES 

9.5.1 This Section Has Been Intentionally Left Blank, 

9.5.2 Structural Design Requirements. 

9.5.2.1 Design Basis. The seismic analysis and design 
procedures to be used in the design of structures and 
their components shall be as prescribed in this Section. 
The structure shall include complete lateral and vertical 
force-resisting systems capable of providing adequate 
strength, stiffness, and energy dissipation capacity to 
withstand the design ground motions within the pre- 
scribed limits of deformation and strength demand. The 
design ground motions shall be assumed to occur along 
any horizontal direction of a structure. The adequacy 
of the structural systems shall be demonstrated through 
the construction of a mathematical model and evaluation 
of this model for the effects of design ground motions. 
The design seismic forces, and their distribution over 
the height of the structure, shall be established in accor- 
dance with one of the applicable procedures indicated 
in Section 9.5.2.5 and the corresponding internal forces 
and deformations in the members of the structure shall 
be determined. An approved alternative procedure shall 
not be used to establish the seismic forces and their dis- 
tribution unless the corresponding internal forces and 
deformations in the members are determined using a 
model consistent with the procedure adopted. 

Individual members shall be provided with adequate 
strength to resist the shears, axial forces, and moments 
determined in accordance with these provisions, and con- 
nections shall develop the strength of the connected 
members or the forces indicated above. The deforma- 
tion of the structure shall not exceed the prescribed 



9.5.2.2 Basic Seismic Force-Resisting Systems, The 
basic lateral and vertical seismic force-resisting sys- 
tem shall conform to one of the types indicated in 
Table 9.5.2.2. Each type is subdivided by the types of 
vertical element used to resist lateral seismic forces. The 
structural system used shall be in accordance with the 
Seismic Design Category and height limitations indi- 
cated in Table 9.5.2.2. The appropriate response mod- 
ification, coefficient, 7?, system overstrength factor, Qq, 
and the deflection amplification factor (Q) indicated in 
Table 9.5.2.2 shall be used in determining the base shear, 
element design forces, and design story drift. Special 
framing requirements are indicated in Section 9.5.2.6 
and Sections 9.8, 9.9, 9.10, 9.11, and 9.1.2 for structures 
assigned to the various Seismic Design Categories. 

Seismic force-resisting systems that are not con- 
tained in Table 9.5.2.2 shall be permitted if analytical 
and test data are submitted that establish the dynamic 
characteristics and demonstrate the lateral force resis- 
tance and energy dissipation capacity to be equiva- 
lent to the structural systems listed in Table 9.5.2.2 for 
equivalent response modification coefficient, R, system 
overstrength coefficient, J3o> and deflection amplification 
factor, Cd, values. 

9.5.2.2.1 Dual System. For a dual system, the 
moment frame shall be capable of resisting at least 
25% of the design seismic forces. The total seismic- 
force resistance is to be provided by the combination 
of the moment frame and the shear walls or braced 
frames in proportion to their rigidities. 

9.5.2.2.2 Combinations of Framing Systems. Dif- 
ferent seismic force-resisting systems are permit- 
ted along the two orthogonal axes of the structure. 
Combinations of seismic force-resisting systems shall 
comply with the requirements of this Section. 



132 



ASCE 7-02 



TABLE 9.5.2.2 
DESIGN COEFFICIENTS AND FACTORS FOR BASIC SEISMIC FORCE-RESISTING SYSTEMS 











Structural System Limitations 

and 
Building Height (ft) Limitations 


Basic SeismiG Force-Resisting System 


Response 

Modification 

Coefficient, R a 


System Over- 
strength 
Factor, S2 9 


Deflection 
Amplification 
Factor, C d b 


Seismic Design Category 


A&B 


C 


D d 


E e 


F e 


Bearing Wall Systems 


















Ordinary steel concentrically braced frames 


4 


2 


3 ] - 

J 2 


NL 


NL 


35 k 


35 k 


NP k 


Special reinforced concrete shear walls 


5 


2 X - 


5 


NL 


NL 


160 


160 


100 


Ordinary reinforced concrete shear walls 


4 


2 l - 


4 


NL 


NL 


NP 


NP 


NP 


Detailed plain concrete shear walls 


A 


2 X - 

Z 2 


2 


NL 


NP 


NP 


NP 


NP 


Ordinary plain concrete shear walls 


4 


2 1 

Z 2 


u 


NL 


NP 


NP 


NP 


NP 


Special reinforced masonry shear walls 


5 


2 X - 

^2 


H 


NL 


NL 


160 


160 


100 


Intermediate reinforced masonry shear walls 


J 2 


2 l - 


H 


NL 


NL 


NP 


NP 


NP 


Ordinary reinforced masonry shear walls 


2 


2± 

^2 


H 


NL 


160 


NP 


NP 


NP 


Detailed plain masonry shear walls 


2 


2 l - 


if 


NL 


NP 


NP 


NP 


NP 


Ordinary plain masonry shear walls 


H 


2 l - 

z 2 


H 


NL 


NP 


NP 


NP 


NP 


Light-framed walls sheathed with wood 
structural panels rated for shear resistance 
or steel sheets 


6 


3 


4 


NL 


NL 


65 


65 


65 


Light-framed walls with shear panels of all 
other materials 


2 


A 


2 


NL 


NL 


35 


NP 


NP 


Light-framed wall systems using flat strap 
bracing 


4 


2 


3 ] ~ 

J 2 


NL 


NL 


65 


65 


65 



Building Frame Systems 

Steel eccentrically braced frames, moment 
resisting, connections at columns away from 
links 


8 


2 


4 


NL 


NL 


160 


160 


100 


Steel eccentrically braced frames, 
non-moment resisting, connections at 
columns away from links 


7 


2 


4 


NL 


NL 


160 


160 


100 


Special steel concentrically braced frames 


6 


2 


5 


NL 


NL 


160 


160 


100 


Ordinary steel concentrically braced frames 


5 


2 


4± 

^2 


NL 


NL 


35 k 


35 k 


NP k 


Special reinforced concrete shear walls 


6 


2 X ~ 

Z 2 


5 


NL 


NL 


160 


160 


100 


Ordinary reinforced concrete shear walls 


5 


2 1 

Z 2 


4^ 

H 2 


NL 


NL 


NP 


NP 


NP 


Detailed plain concrete shear walls 


3 


2 { - 


2 { - 

^2 


NL 


NP 


NP 


NP 


NP 


Ordinary plain concrete shear walls 


2 


2 ] - 

L 2 


2 


NL 


NP 


NP 


NP 


NP 


Composite eccentrically braced frames 


8 


2 


4 


NL 


NL 


160 


160 


100 


Composite concentrically braced frames 


5 


2 


^2 


NL 


NL 


160 


160 


100 


Ordinary composite braced frames 


3 


2 


3 


NL 


NL 


NP 


NP 


NP 


Composite steel plate shear walls 


^ 


2- 

L 2 


5\ 


NL 


NL 


160 


160 


100 


Special composite reinforced concrete shear 
walls with steel elements 


6 


2 X - 

^2 


5 


NL 


NL 


160 


160 


100 


Ordinary composite reinforced concrete 
shear walls with steel elements 


5 


2 X - 

Z 2 


H 


NL 


NL 


NP 


NP 


NP 


Special reinforced masonry shear walls 


5i 


2 l - 

A 2 


4 


NL 


NL 


160 


160 


100 


Intermediate reinforced masonry shear walls 


4 


2 X ~ 

Z 2 


4 


NL 


NL 


NP 


NP 


NP 


Ordinary reinforced masonry shear walls 


A 


2 ] ~ 

2 


H 


NL 


160 


NP 


NP 


NP 



Minimum Design Loads for Buildings and Other Structures 



133 



TABLE 9.5.2.2 — continued 
DESIGN COEFFICIENTS AND FACTORS FOR BASIC SEISMIC FORCE-RESISTING SYSTEMS 



Basic Seismic Force-Resisting System 


Response 

Modification 

Coefficient, R a 


System Over- 
strength 
Factor, W $ 


Deflection 
Amplification 
Factor, C d b 


Structural System Limitations 

and 
Building Height (ft) Limitations 


Seismic Design Category 


A&B 


C 


D d 


E e 


F e 


Detailed plain masonry shear walls 


A 


2 ] - 

2 


A 


NL 


160 


NP 


NP 


NP 


Ordinary plain masonry shear walls 


4 


2 ] - 

2 


i* 


NL 


NP 


NP 


NP 

65 


NP 


Light-framed walls sheathed with wood 
structural panels rated for shear resistance 
or steel sheets 


H 


A 


<4 


NL 


NL 


65 


65 


65 


Light-framed walls with shear panels of all 
other materials 


A 


A 


H 


NL 


NL 


35 


NP 


NP 



Moment Resisting Frame Systems 


















Special steel moment frames 


8 


3 


H 


NL 


NL 


NL 


NL 


NL 


Special steel truss moment frames 


7 


3 


H 


NL 


NL 


160 


100 


NP 


Intermediate steel moment frames 


4.5 


3 


4 


NL 


NL 


35 h 


Np h,i 


NF h,i 


Ordinary steel moment frames 


3.5 


3 


3 


NL 


NL 


N ph : . 


Np hj 


N ph,i 


Special reinforced concrete moment frames 


8 


3 


5^ 


NL 


NL 


NL 


NL 


NL 


Intermediate reinforced concrete moment 
frames 


5 


3 


4 


NL 


NL 


NP 


NP 


NP 


Ordinary reinforced concrete moment 
frames 


3 


3 


21 


NL 


NP 


NP 


NP 


NP 


Special composite moment frames 


8 


3 


5^ 


NL 


NL 


NL 


NL 


NL 


Intermediate composite moment frames 


5 


3 


4 


NL 


NL 


NP 


NP 


NP 


Composite partially restrained moment 
frames 


6 


3 


H 


160 


160 


100 


NP 


NP 


Ordinary composite moment frames 


3 


3 


2 X - 

2 


NL 


NP 


NP 


NP 


NP 


Special masonry moment frames 


H 


3 


5 


NL 


NL 


160 


160 


100 



Dual Systems with Special Moment 
Frames Capable of Resisting at Least 
25% of Prescribed Seismic Forces 


















Steel eccentrically braced frames, moment 
resisting connections, at columns away from 
links 


8 


H 


4 


NL 


NL 


NL 


NL 


NL 


Steel eccentrically braced frames, 
non-moment resisting connections, at 
columns away from links 


7 


H 


4 


NL 


NL 


NL 


NL 


NL 


Special steel concentrically braced frames 


8 


"2 


H 


NL 


NL 


NL 


NL 


NL 


Special reinforced concrete shear walls 


8 


H 


61 


NL 


NL 


NL 


NL 


NL 


Ordinary reinforced concrete shear walls 


7 


2 ] - 

^2 


6 


NL 


NL 


NP 


NP 


NP 


Composite eccentrically braced frames 


8 


2 1 


4 


NL 


NL 


NL 


NL 


NL 


Composite concentrically braced frames 


6 


9i 

"2 


5 


NL 


NL 


NL 


NL 


NL 


Composite steel plate shear walls 


8 


^2 


<4 


NL 


NL 


NL 


NL 


NL 


Special composite reinforced concrete shear 
walls with steel elements 


8 


2-i 

Z 2 


61 


NL 


NL 


NL 


NL 


NL 



134 



ASCE 7-02 



TABLE 9.5.2.2 - continued 
DESIGN COEFFICIENTS AND FACTORS FOR BASIC SEISMIC FORCE-RESISTING SYSTEMS 











Structural System 


Limitations 


Basic Seismic Force-Resisting System 


Response 

Modification 

Coefficient, R B 


System Over- 
strength 
Factor, W Q 9 


Deflection 
Amplification 
Factor, C d b 


Building Height {ft} Limitations 


Seismic Design Category 


A&B 


C 


D d 


E e 


F e 


Ordinary composite reinforced concrete 
shear walls with steel elements 


1 


2\ 


6 


NL 


NL 


NP 


NP 


NP 


Special reinforced masonry shear walls 


1 


3 


H 


NL 


NL 


NL 


NL 


NL 


Intermediate reinforced masonry shear walls 


6 


2 ] - 

^2 


5 


NL 


NL 


NL 


NL 


NL 


Ordinary steel concentrically braced frames 


6 


2 X ~ 


5 


NL 


NL 


NL 


NL 


NL 


Dual Systems with Intermediate Moment 
Frames Capable of Resisting at Least 
25% of Prescribed Seismic Forces 


















Special steel concentrically braced frames* 


4± 

^2 


H 


4! 


NL 


NL 


35 


NP 


NP h ' j 


Special reinforced concrete shear walls 


6 


A 


5 


NL 


NL 


160 


100 


100 


Ordinary reinforced masonry shear walls 


3 


3 


2 { - 
^2 


NL 


160 


NP 


NP 


NP 


Intermediate reinforced masonry shear walls 


5 


3 


^2 


NL 


NL 


NP 


NP 


NP 


Composite concentrically braced frames 


5 


21 


4 ] - 

2 


NL 


NL 


160 


100 


NP 


Ordinary composite braced frames 


4 


A 


3 


NL 


NL 


NP 


NP 


NP 


Ordinary composite reinforced concrete 
shear walls with steel elements 


5 


3 


H 


NL 


NL 


NP 


NP 


NP 


Ordinary steel concentrically braced frames 


5 


2 ] ~ 


4| 


NL 


NL 


160 


100 


NP 


Ordinary reinforced concrete shear walls 


H 


"2 


4! 

^2 


NL 


NL 


NP 


NP 


NP 


Inverted Pendulum Systems and 
Cantilevered Column Systems 


















Special steel moment frames 


2\ 


2 


w 2 


NL 


NL 


NL 


NL 


NL 


Ordinary steel moment frames 


H 


2 


A 


NL 


NL 


NP 


NP 


NP ■ 


Special reinforced concrete moment frames 


2 { ~ 
^2 


2 


n 


NL 


NL 


NL 


NL 


NL 


Structural Steel Systems Not Specifically 
Detailed for Seismic Resistance 


3 


3 


3 


NL 


NL 


NP 


NP 


NP 



a Response modification coefficient, R, for use throughout the standard. Note R reduces forces to a strength level, not an allowable stress level. 

b Deflection amplification factor, Cd, for use in Sections 9.5.3.7.1 and 9.5.3.7.2 

c NL = Not Limited and NP = Not Permitted. For metric units use 30 m for 100 ft and use 50 m for 160 ft. Heights are measured from the base of 

the structure as defined in Section 9.2.1. 

d See Section 9.5.2.2.4.1 for a description of building systems limited to buildings with a height of 240 ft (75 m) or less. 

e See Sections 9.5.2.2.4 and 9.5.2.2.4.5 for building systems limited to buildings with a height of 160 ft (50 m) or less. 

f Ordinary moment frame is permitted to be used in lieu of intermediate moment frame in Seismic Design Categories B and C. 

g The tabulated value of the overstrength factor, Wq, may be reduced by subtracting | for structures with flexible diaphragms but shall not be taken as 

less than 2.0 for any structure. 

h Steel ordinary moment frames and intermediate moment frames are permitted in single-story buildings up to a height of 60 ft, when the moment joints 

of field connections are constructed of bolted end plates and the dead load of the roof does not exceed 15 psf. 

1 Steel ordinary moment frames are permitted in buildings up to a height of 35 ft where the dead load of the walls, floors, and roofs does not exceed 

15 psf. 

k Steel ordinary concentrically braced frames are permitted in single-story buildings up to a height of 60 ft when the dead load of the roof does not 

exceed 15 psf and in penthouse structures. 



Minimum Design Loads for Buildings and Other Structures 



135 



9.5.2.2.2.1 R and ^ Factors. The response mod- 
ification, coefficient, R, in the direction under 
consideration at any story shall not exceed the 
lowest response modification coefficient, R, for 
the seismic force-resisting system in the same 
direction considered above that story excluding 
penthouses. For other than dual systems, where a 
combination of different structural systems is uti- 
lized to resist lateral forces in the same direction, 
the value of R used in that direction shall not be 
greater than the least value of any of the systems 
utilized in the same direction. If a system other 
than a dual system with a response modification 
coefficient, R, with a value of less than 5 is used 
as part of the seismic force-resisting system in any 
direction of the structure, the lowest such value 
shall be used for the entire structure. The system 
overstrength factor, £2 , in the direction under con- 
sideration at any story shall not be less than the 
largest value of this factor for the seismic force- 
resisting system in the same direction considered 
above that story. 

Exceptions: 

1. The limit does not apply to supported 
structural systems with a weight equal 
to or less than 10% of the weight of 
the structure. 

2. Detached one- and two-family dwellings 
of light-frame construction. 

9.5.2.2.2.2 Combination Framing Detailing 
Requirements. The detailing requirements of 
Section 9.5.2.6 required by the higher response 
modification coefficient, R, shall be used for struc- 
tural components common to systems having dif- 
ferent response modification coefficients. 



this Section. In such buildings the braced frames 
or cast-in-place special reinforced concrete shear 
walls in any one plane shall resist no more than 
60% of the total seismic forces in each direction, 
neglecting torsional effects. The seismic force in 
any braced frame or shear wall in any one plane 
resulting from torsional effects shall not exceed 
20% of the total seismic force in that braced frame 
or shear wall. 

9.5.2.2.4.2 Interaction Effects. Moment resisting 
frames that are enclosed or adjoined by more 
rigid elements not considered to be part of the 
seismic force-resisting system shall be designed so 
that the action or failure of those elements will 
not impair the vertical load and seismic force- 
resisting capability of the frame. The design shall 
provide for the effect of these rigid elements 
on the structural system at structure deformations 
corresponding to the design story drift (A) as 
determined in Section 9.5.3.7. In addition, the 
effects of these elements shall be considered when 
determining whether a structure has one or more 
of the irregularities defined in Section 9.5.23. 

9.5.2.2.4.3 Deformational Compatibility. Every 
structural component not included in the seismic 
force-resisting system in the direction under con- 
sideration shall be designed to be adequate for 
the vertical load-carrying capacity and the induced 
moments and shears resulting from the design 
story drift (A) as determined in accordance with 
Section 9.5.3.7; see also Section 9.5.2.8. 

Exception: Reinforced concrete frame mem- 
bers not designed as part of the seismic force- 
resisting system shall comply with Section 21.9 
of Ref. 9.9-1. 



9.5.2.23 Seismic Design Categories B and C. The 
structural framing system for structures assigned to 
Seismic Design Categories B and C shall comply 
with the structure height and structural limitations in 
Table 9.5.2.2. 

9.5.2.2.4 Seismic Design Categories D and E, The 
structural framing system for a structure assigned to 
Seismic Design Categories D and E shall comply 
with Section 9.5.2.2.3 and the additional provisions 
of this Section, 

9.5.2.2.4.1 Increased Building Height Limit. The 
height limits in Table 9.5.2.2 are permitted to 
be increased to 240 ft (75 m) in buildings that 
have steel braced frames or concrete cast-in-place 
shear walls and that meet the requirements of 



When determining the moments and shears 
induced in components that are not included in 
the seismic force-resisting system in the direc- 
tion under consideration, the stiffening effects of 
adjoining rigid structural and nonstructural ele- 
ments shall be considered and a rational value of 
member and restraint stiffness shall be used. 

9.5.2.2.4.4 Special Moment Frames. A special 
moment frame that is used but not required 
by Table 9.5.2.2 shall not be discontinued and 
supported by a more rigid system with a 
lower response modification coefficient (R) unless 
the requirements of Sections 9.5.2.6.2.4 and 
9.5.2.6.4.2 are met. Where a special moment frame 
is required by Table 9.5.2.2, the frame shall be 
continuous to the foundation. 



136 



ASCE 7-02 



9.5.2.2,5 Seismic Design Category F. The framing 
systems of structures assigned to Seismic Design 
Category F shall conform to the requirements of 
Section 9.5.2.2.4 for Seismic Design Categories D 
and E and to the additional requirements and lim- 
itations of this Section. The increased height limit 
of Section 9.5.2.2.4.1 for braced frame or shear wall 
systems shall be reduced from 240 ft (75 m) to 160 ft 
(50 m). 

9.5.2.3 Structure Configuration. Structures shall be 
classified as regular or irregular based on the criteria 
in this Section. Such classification shall be based on the 
plan and vertical configuration. 

9.5.2.3.1 Diaphragm Flexibility. A diaphragm shall 
be considered flexible for the purposes of distribution 
of story shear and torsional moment when the com- 
puted maximum in-plane deflection of the diaphragm 



itself under lateral load is more than two times the 
average drift of adjoining vertical elements of the 
lateral force-resisting system of the associated story 
under equivalent tributary lateral load. The loadings 
used for this calculation shall be those prescribed by 
Section 9.5.5. 

9.5.2.3.2 Plan Irregularity. Structures having one or 
more of the irregularity types listed in Table 9.5.2.3.2 
shall be designated as having plan structural irregu- 
larity. Such structures assigned to the Seismic Design 
Categories listed in Table 9.5.2.3.2 shall comply 
with the requirements in the sections referenced in 
that table. 

9.5.2.3.3 Vertical Irregularity. Structures having 
one or more of the irregularity types listed in 
Table 9.5.2.3.3 shall be designated as having vertical 
irregularity. Such structures assigned to the Seismic 



TABLE 9.5.2.3.2 
PLAN STRUCTURAL IRREGULARITIES 



Irregularity Type and Description 


Reference 
Section 


Seismic Design 

Category 

Application 


la. 


Torsional Irregularity 

Torsional irregularity is defined to exist where the maximum story drift, 
computed including accidental torsion, at one end of the structure 
transverse to an axis is more than 1.2 times the average of the story 
drifts at the two ends of the structure. Torsional irregularity requirements 
in the reference sections apply only to structures in which the 
diaphragms are rigid or semirigid. 


9.5.2.6.4.2 
9.5.5.5.2 


D, E, and F 
C, D, E, and F 


lb. 


Extreme Torsional Irregularity 

Extreme Torsional Irregularity is defined to exist where the maximum 
story drift, computed including accidental torsion, at one end of the 
structure transverse to an axis is more than 1 .4 times the average of the 
story drifts at the two ends of the structure. Extreme torsional 
irregularity requirements in the reference sections apply only to 
structures in which the diaphragms are rigid or semirigid. 


9.5.2.6.4.2 

9.5.5.5.2 

9.5.2.6.5.1 


D 
CandD 
E and F 


2. 


Re-entrant Corners 

Plan configurations of a structure and its lateral force-resisting system 
contain re-entrant corners, where both projections of the structure 
beyond a re-entrant comer are greater than 15% of the plan dimension 
of the structure in the given direction. 


9.5.2.6.4.2 


D, E, and F 


3. 


Diaphragm Discontinuity 

Diaphragms with abrupt discontinuities or variations in stiffness, 
including those having cutout or open areas greater than 50% of the 
gross enclosed diaphragm area, or changes in effective diaphragm 
stiffness of more than 50% from one-story to the next. 


9,5.2.6.4.2 


D, E, and F 


4. 


Out-of-Plane Offsets 

Discontinuities in a lateral force-resistance path, such as out-of-plane 

offsets of the vertical elements. 


9.5.2.6.4.2 
9.5.2.6.2.11 


D, E, and F 
B, C, D, E, or F 


5. 


Nonparallel Systems 

The vertical lateral force-resisting elements are not parallel to or 

symmetric about the major orthogonal axes of the lateral force-resisting 

system. 


9.5.2.6.3.1 


C, D, E, and F 



Minimum Design Loads for Buitdings and Other Structures 



137 



TABLE 9.5.2.3.3 
VERTICAL STRUCTURAL IRREGULARITIES 



Irregularity Type and Description 


Reference 
Section 


Seismic Design 

Category 

Application 


la. 


Stiffness Irregularity: Soft Story 

A soft story is one in which the lateral stiffness is less than 70% of that 
in the story above or less than 80% of the average stiffness of the three 
stories above. 


9.5.2.5 1 


D, E, and F 


lb. 


Stiffness Irregularity: Extreme Soft Story 

An extreme soft story is one in which the lateral stiffness is less than 
60% of that in the story above or less than 70% of the average stiffness 
of the three stories above. 


9.5.2.5.1 
9.5.2.6.5.1 


D, 
E and F 


2. 


Weight (Mass) Irregularity 

Mass irregularity shall be considered to exist where the effective mass 
of any story is more than 150% of the effective mass of an adjacent 
story. A roof that is lighter than the floor below need not be considered. 


9.5.2.5.1 


D, E, and F 


3. 


Vertical Geometric Irregularity 

Vertical geometric i regularity shall be considered to exist where the 
horizontal dimension of the lateral force-resisting system in any story is 
more than 130% of that in an adjacent story. 


9.5.2.5.1 


D, E, and F 


4. 


In-Plane Discontinuity in Vertical Lateral Force-Resisting Elements 
In-plane discontinuity in vertical lateral force-resisting elements shall be 
considered to exist where an in-plane offset of the lateral force-resisting 
elements is greater than the length of those elements or there exists a 
reduction in stiffness of the resisting element in the story below. 


9.5.2.6.2.11 
9.5.2.6.4.2 


B, C, D, E, and F 

D, E, and F 


5. 


Discontinuity in Lateral Strength: Weak Story 

A weak story is one in which the story lateral strength is less than 80% 

of that in the story above. The story strength is the total strength of all 

seismic-resisting elements sharing the story shear for the direction under 

consideration. 


9.5.2.6.2.2 
9.5.2.6.5.1 


B, C, D, E, and F 

E and F 



Design Categories listed in Table 9.5.2.3.3 shall com- 
ply with the requirements in the sections referenced 
in that table. 



Exceptions: 

1. Vertical structural irregularities of Types la, 
lb, or 2 in Table 9.5.2.3.3 do not apply 
where no story drift ratio under design 
lateral seismic force is greater than 130% of 
the story drift ratio of the next story above. 
Torsional effects need not be considered in 
the calculation of story drifts. The story drift 
ratio relationship for the top 2 stories of the 
structure are not required to be evaluated. 

2. Irregularities Types la, lb, and 2 of 
Table 9.5.2.3.3 are not required to be 
considered for 1 -story buildings in any 
Seismic Design Category or for 2-story 
buildings in Seismic Design Categories A, 
B, C, or D. 



9.5.2,4 Redundancy. A reliability factor, p, shall be 
assigned to all structures in accordance with this Section, 
based on the extent of structural redundancy inherent in 
the lateral force-resisting system. 

9.5.2.4.1 Seismic Design Categories A, B, and C. 
For structures in Seismic Design Categories A, B, and 
C, the value of p is 1.0. 

9.5.2.4.2 Seismic Design Category D. For structures 
in Seismic Design Category D, p shall be taken as the 
largest of the values of p x calculated at each story 
"x" of the structure in accordance with Eq. 9.5.2.4.2- 
1 as follows: 



Px =2- 



20 



(Eq. 9.5.2.4.24) 



where 



= the ratio of the design story shear resisted 
by the single element carrying the most 
shear force in the story to the total story 
shear, for a given direction of loading. For 



138 



ASCE 7-02 



braced frames, the value of r maXx is equal to 
the lateral force component in the most 
heavily loaded brace element divided by the 
story shear. For moment frames, r maXx shall 
be taken as the maximum of the sum of the 
shears in any two adjacent columns in the 
plane of a moment frame divided by the 
story shear. For columns common to two 
bays with moment resisting connections on 
opposite sides at the level under 
consideration, 70% of the shear in that 
column may be used in the column shear 
summation. For shear walls, r maXx shall be 
taken equal to shear in the most heavily 
loaded wall or wall pier multiplied by \0/l w 
(the metric coefficient is 33/l w ) where l w is 
the wall or wall pier length in ft (m) 
divided by the story shear and where the 
ratio 10// w need not be taken greater than 
1.0 for buildings of light-frame 
construction. For dual systems, r maXx shall 
be taken as the maximum value as defined 
above considering all lateral-load-resisting 
elements in the story. The lateral loads shall 
be distributed to elements based on relative 
rigidities considering the interaction of the 
dual system. For dual systems, the value of 
p need not exceed 80% of the value 
calculated above. 
A x = the floor area in ft 2 of the diaphragm level 
immediately above the story 

The value of p need not exceed 1.5, which may 
be used for any structure. The value of p shall not be 
taken as less than 1.0. 

Exception: For structures with lateral-force- 
resisting systems in any direction consisting 
solely of special moment frames, the lateral-force- 
resisting system shall be configured such that the 
value of p calculated in accordance with this 
Section does not exceed 1.25. 

The metric equivalent of Eq. 9.5.2.4.2 is: 

6.1 



Px - 2 ■ 



(Eq. 9.5.2.4.2) 



solely of special moment frames, the lateral-force- 
resisting system shall be configured such that 
the value of p calculated in accordance with 
Section 9.5.2.4.2 does not exceed l.L 

9.5.2.5 Analysis Procedures. A structural analysis con- 
forming to one of the types permitted in Section 9.5.2.5. 1 
shall be made for all structures. Application of load- 
ing shall be as indicated in Section 9.5.2.5,2.1, and as 
required by the selected analysis procedure. All mem- 
bers of the structure's seismic force-resisting system and 
their connections shall have adequate strength to resist 
the forces, Q E , predicted by the analysis, in combina- 
tion with other loads, as required by Section 9.5.2.7. 
Drifts predicted by the analysis shall be within the lim- 
its specified by Section 9.5.2.8. If a nonlinear analysis 
is performed, component deformation demands shall not 
exceed limiting values as indicated in Section 9.5.7.3.2. 

Exception: For structures designed using the index 
force analysis procedure of Section 9.5.3 or the sim- 
plified analysis procedure of Section 9.5.4, drift need 
not be evaluated. 

9.5.2.5.1 Analysis Procedures. The structural anal- 
ysis required by Section 9.5.2.5 shall consist of one 
of the types permitted in Table 9.5.2.5.1, based on 
the structure's Seismic Design Category, structural 
system, dynamic properties and regularity, or with 
the approval of the authority having jurisdiction, an 
alternative generally accepted procedure shall be per- 
mitted to be used. 

9.5.2.5.2 Application of Loading. The directions of 
application of seismic forces used in the design shall 
be those which will produce the most critical load 
effects. It shall be permitted to satisfy this requirement 
using the procedures of Section 9.5.2.5.2.1 for Seis- 
mic Design Category A and B, Section 9.5.2.5.2.2 for 
Seismic Design Category C, and Section 9.5.2.5.2.3 
for Seismic Design Categories D, E, and F. All struc- 
tural components and their connections shall be pro- 
vided with strengths sufficient to resist the effects of 
the seismic forces prescribed herein. Loads shall be 
combined as prescribed in Section 9.5.2.7. 



where A x is in m 2 . 

9.5.2.4.3 Seismic Design Categories E and F. For 
structures in Seismic Design Categories E and F, 
the value of r shall be calculated as indicated in 
Section 9.5.2.4.2, above. 



9.5.2.5.2.1 Seismic Design Categories A and B. 
For structures assigned to Seismic Design Cate- 
gory A and B, the design seismic forces are per- 
mitted to be applied separately in each of two 
orthogonal directions and orthogonal interaction 
effects may be neglected. 



Exception: For structures with lateral force- 
resisting systems in any direction consisting 



9.5.2.5.2.2 Seismic Design Category C. Loading 
applied to structures assigned to Seismic Design 



Minimum Design Loads for Buildings and Other Structures 



139 



TABLE 9.5.2.5.1 
PERMITTED ANALYTICAL PROCEDURES 



Seismic 

Design 

Category 


Structural 
Characteristics 


Index 

Force 

Analysis 

Section 9.5.3 


Simplified 

Analysis 

Section 9.5.4 


Equivalent 

Lateral 

Force 

Analysis 

Section 9.5.5 


Modal 

Response 

Spectrum 

Analysis 

Section 9.5.6 


Linear 

Response 

History 

Analysis 

Section 9.5.7 


Moniinear 

Response 

History 

Analysis 

Section 9.5.8 


A 


All structures 


P 


P 


P 


P 


P 


P 


B,C 


SUG-1 buildings of 
light-framed construction 
not exceeding three 
stories in height 


NP 


P 


P 


P 


P 


P 


Other SUG-1 buildings 
not exceeding two 
stories in height 


NP 


P 


P 


P 


P 


P 


All other structures 


NP 


NP 


P 


P 


P 


P 


D, E, F 


SUG-1 buildings of 
light-framed construction 
not exceeding three 
stories in height 


NP 


P 


P 


P 


P 




Other SUG-1 buildings 
not exceeding two 
stories in height 


NP 


P 


P 


P 


P 


P 


Regular structures with 
T< 3.5 T, and all 
structures of light-frame 
construction 


NP 


NP 


P 


P 


P 


P 


Irregular structures with 
T <3.5 T, and having 
only plan irregularities 
type 2, 3, 4, or 5 of 
Table 9.5.2.3.2 or 
vertical irregularities 
type 4 or 5 of 
Table 9.5.2.3.3 


NP 


NP 


P 


P 


P 


P 


All other structures 


NP 


NP 


NP 


P 


P 


P 



Notes: P — indicates permitted, NP — indicates not permitted 



Category C shall, as a minimum, conform to the 
requirements of Section 9.5.2.5.2.1 for Seismic 
Design Categories A and B and the requirements 
of this Section. Structures that have plan struc- 
tural irregularity Type 5 in Table 9.5.2.3.2 shall 
be analyzed for seismic forces using a three- 
dimensional representation and either of the fol- 
lowing procedures: 

a. The structure shall be analyzed using the 
equivalent lateral force analysis procedure 
of Section 9.5.5, the modal response spec- 
trum analysis procedure of Section 9.5.6, 
or the linear response history analysis 
procedure of Section 9.5.7, as permitted 
under Section 9.5.2.5.1, with the loading 
applied independently in any two orthogonal 



directions and the most critical load effect 
due to direction of application of seismic 
forces on the structure may be assumed to 
be satisfied if components and their founda- 
tions are designed for the following combina- 
tion of prescribed loads: 100% of the forces 
for one direction plus 30% of the forces for 
the perpendicular direction; the combination 
requiring the maximum component strength 
shall be used. 

b. The structure shall be analyzed using the 
linear response history analysis procedure 
of Section 9.5.7 or the nonlinear response 
history analysis procedure of Section 9.5.8, 
as permitted by Section 9.5.2.5.1, with 



140 



ASCE 7-02 



orthogonal pairs of ground motion acceler- 
ation histories applied simultaneously. 

9.5.2.5.23 Seismic Design Categories D, E 9 and 
F. Structures assigned to Seismic Design Cate- 
gories D, E, and F shall, as a minimum, conform 
to the requirements of Section 9.5.2.5.2.2 In addi- 
tion, any column or wall that forms part of two or 
more intersecting seismic force-resisting systems 
and is subjected to axial load due to seismic forces 
acting along either principal plan axis equaling or 
exceeding 20% of the axial design strength of the 
column or wall shall be designed for the most 
critical load effect due to application of seismic 
forces in any direction. Either of the procedures 
of Section 9.5.2.5.2a or b shall be permitted to be 
used to satisfy this requirement. Two-dimensional 
analyses shall be permitted for structures with flex- 
ible diaphragms. 

9.5.2.6 Design and Detailing Requirements. The 
design and detailing of the components of the seis- 
mic force-resisting system shall comply with the 
requirements of this Section. Foundation design shall 
conform to the applicable requirements of Section 9.7. 
The materials and the systems composed of those 
materials shall conform to the requirements and 
limitations of Sections 9.8 through 9.12 for the 
applicable category. 

9*5*2.6*1 Seismic Design Category A. The design 
and detailing of structures assigned to Category A 
shall comply with the requirements of this Section. 

9.5.2.6.1.1 Load Path Connections. All parts of 
the structure between separation joints shall be 
interconnected to form a continuous path to the 
seismic force-resisting system, and the connec- 
tions shall be capable of transmitting the seismic 
force (F p ) induced by the parts being connected. 
Any smaller portion of the structure shall be tied 
to the remainder of the structure with elements 
having a design strength capable of transmitting 
a seismic force of 0.133 times the short period 
design spectral response acceleration coefficient, 
Sns> times the weight of the smaller portion or 
5% of the portion's weight, whichever is greater. 
This connection force does not apply to the overall 
design of the lateral-force-resisting system. Con- 
nection design forces need not exceed the maxi- 
mum forces that the structural system can deliver 
to the connection. 

A positive connection for resisting a horizontal 
force acting parallel to the member shall be pro- 
vided for each beam, girder, or truss to its support. 



The connection shall have a minimum strength of 
5% of the dead plus live load reaction. One means 
to provide the strength is to use connecting ele- 
ments such as slabs. 

9.5.2.6.1.2 Anchorage of Concrete or Masonry 
Walls. Concrete and masonry walls shall be 
anchored to the roof and all floors and members 
that provide lateral support for the wall or which 
are supported by the wall. The anchorage shall pro- 
vide a direct connection between the walls and the 
roof or floor construction. The connections shall be 
capable of resisting the horizontal forces specified 
in Section 9.5.2.6.1.1 but not less than a minimum 
strength level, horizontal force of 280 lbs/ linear ft 
(4.09 kN/m) of wall substituted for E in the load 
combinations of Section 2.3.2 or 2.4.1. 

9.5.2.6.2 Seismic Design Category B. Structures 
assigned to Seismic Design Category B shall con- 
form to the requirements of Section 9.5.2.6.1 for 
Seismic Design Category A and the requirements of 
this Section. 

9.5.2.6.2.1 P-Delta Effects. P-delta effects shall 
be included where required by Section 9.5.5.7.2. 

9.5.2.6.2.2 Openings. Where openings occur in 
shear walls, diaphragms, or other plate-type ele- 
ments, reinforcement at the edges of the openings 
shall be designed to transfer the stresses into the 
structure. The edge reinforcement shall extend into 
the body of the wall or diaphragm a distance suffi- 
cient to develop the force in the reinforcement. The 
extension must be sufficient in length to allow dis- 
sipation or transfer of the force without exceeding 
the shear and tension capacity of the diaphragm or 
the wall. 

9.5.2.6.23 Direction of Seismic Load. The direc- 
tion of application of seismic forces used in design 
shall be that which will produce the most criti- 
cal load effect in each component. This require- 
ment will be deemed satisfied if the design seismic 
forces are applied separately and independently in 
each of two orthogonal directions. 

9.5.2.6.2.4 Discontinuities in Vertical System. 
Structures with a discontinuity in lateral capac- 
ity, vertical irregularity Type 5 as defined in 
Table 9.5.2.3.3, shall not be more than 2 stories 
or 30 ft (9 m) in height where the "weak" story 
has a calculated strength of less than 65% of the 
story above. 



Minimum Design Loads for Buildings and Other Structures 



141 



Exception: The limit does not apply where 
the "weak" story is capable of resisting a total 
seismic force equal to £2 times the design force 
prescribed in Section 9.5.3. 

9.5.2.6.2.5 Nonredundant Systems. The design 
of a structure shall consider the potentially adverse 
effect that the failure of a single member, connec- 
tion, or component of the seismic force-resisting 
system will have on the stability of the structure; 
see Section 1.4. 

9.5.2.6.2.6 Collector Elements. Collector ele- 
ments shall be provided that are capable of 
transferring the seismic forces originating in other 
portions of the structure to the element providing 
the resistance to those forces. 

9.5.2.6.2.7 Diaphragms. The deflection in the 
plane of the diaphragm, as determined by engi- 
neering analysis, shall not exceed the permissible 
deflection of the attached elements. Permissible 
deflection shall be that deflection which will per- 
mit the attached element to maintain its structural 
integrity under the individual loading and continue 
to support the prescribed loads. 

Floor and roof diaphragms shall be designed to 
resist F p where F p is the larger of: 

1. The portion of the design seismic force at 
the level of the diaphragm that depends on 
the diaphragm for transmission to the ver- 
tical elements of the seismic force-resisting 
system, or 



2. F n 



0.2S DS Iw p + V px 



(Eq. 9.5.2.6.2.7) 



where 



F p = the seismic force induced by 

the parts 
/ — occupancy importance factor 

(Table 9.1.4) 
Sds = the short period site design spectral 

response acceleration coefficient, 

Section 9.4.1 
w p = the weight of the diaphragm and 

other elements of the structure 

attached to it 
V px = the portion of the seismic shear 

force at the level of the diaphragm, 

required to be transferred to the 

components of the vertical seismic 

force-resisting system 

because of the offsets or changes in 

stiffness of the vertical components 

above or below the diaphragm 



Diaphragms shall be designed for both the shear 
and bending stresses resulting from these forces. 
Diaphragms shall have ties or struts to distribute 
the wall anchorage forces into the diaphragm. 
Diaphragm connections shall be positive, mechan- 
ical, or welded type connections. 

At diaphragm discontinuities, such as open- 
ings and re-entrant corners, the design shall 
ensure that the dissipation or transfer of edge 
(chord) forces combined with other forces in the 
diaphragm is within shear and tension capacity of 
the diaphragm. 

9.5.2.6.2.8 Anchorage of Concrete or Masonry 
Walls. Exterior and interior bearing walls and their 
anchorage shall be designed for a force normal 
to the surface equal to 40% of the short period 
design spectral response acceleration, So$> times 
the occupancy importance factor, /, multiplied by 
the weight of wall ( W c ) associated with the anchor, 
with a minimum force of 10% of the weight of the 
wall. Interconnection of wall elements and con- 
nections to supporting framing systems shall have 
sufficient ductility, rotational capacity, or sufficient 
strength to resist shrinkage, thermal changes, and 
differential foundation settlement when combined 
with seismic forces. The connections shall also sat- 
isfy Section 9.5.2.6.1.2. 

The anchorage of concrete or masonry walls to 
supporting construction shall provide a direct con- 
nection capable of resisting the greater of the force 
0.4 S DS IW C as given above or 400 S DS I lbs/linear 
ft (5.84 S D sl kN/m) of wall or the force specified 
in Section 9.5.2.6.1.2. Walls shall be designed to 
resist bending between anchors where the anchor 
spacing exceeds 4 ft (1219 mm). 

9.5.2.6.2.9 Inverted Pendulum-Type Structures. 
Supporting columns or piers of inverted pendulum- 
type structures shall be designed for the bending 
moment calculated at the base determined using 
the procedures given in Section 9.5.3 and varying 
uniformly to a moment at the top equal to one-half 
the calculated bending moment at the base. 

9.5.2.6.2.10 Anchorage of Nonstructural Sys- 
tems. When required by Section 9.6, all portions 
or components of the structure shall be anchored 
for the seismic force, F p , prescribed therein. 

9.5.2.6.2.11 Elements Supporting Discontinu- 
ous Walls or Frames. Columns, beams, trusses, 
or slabs supporting discontinuous walls or frames 
of structures having plan irregularity Type 4 of 
Table 9.5.2.3.2 or vertical irregularity Type 4 of 



142 



ASCE 7-02 



Table 9.5.2.3.3 shall have the design strength to 
resist the maximum axial force that can develop 
in accordance with the special seismic loads of 
Section 9.5.2.7.1. 

9.5.2.6.3 Seismic Design Category C. Structures 
assigned to Category C shall conform to the require- 
ments of Section 9.5.2.6,2 for Category B and to the 
requirements of this Section. 

9.5.2.6.3.1 Collector Elements. Collector ele- 
ments shall be provided that are capable of trans- 
ferring the seismic forces originating in other 
portions of the structure to the element provid- 
ing the resistance to those forces. Collector ele- 
ments, splices, and their connections to resisting 
elements shall resist the special seismic loads of 
Section 9.5.2.7.1. 

Exception: In structures or portions thereof 
braced entirely by light-frame shear walls, 
collector elements, splices, and connections to 
resisting elements need only be designed to resist 
forces in accordance with Section 9.5.2.6.4.4. 

The quantity QqE in Eq. 9.5.2.7.1-1 need not 
exceed the maximum force that can be transferred 
to the collector by the diaphragm and other ele- 
ments of the lateral force-resisting system. 

9.5.2.6.3.2 Anchorage of Concrete or Masonry 
Walls. Concrete or masonry walls shall be 
anchored to all floors, roofs, and members that 
provide out-of-plane lateral support for the wall 
or that are supported by the wall. The anchorage 
shall provide a positive direct connection between 
the wall and floor, roof, or supporting member 
capable of resisting horizontal forces specified in 
this Section for structures with flexible diaphragms 
or with Section 9.6.1.3 (using a p of 1.0 and R p 
of 2.5) for structures with diaphragms that are 
not flexible. 

Anchorage of walls to flexible diaphragms shall 
have the strength to develop the out-of-plane force 
given by Eq. 9.5.2.6.3.2: 



W p = the weight of the wall tributary to 
the anchor 

Diaphragms shall be provided with continuous 
ties or struts between diaphragm chords to dis- 
tribute these anchorage forces into the diaphragms. 
Added chords may be used to form subdiaphragms 
to transmit the anchorage forces to the main con- 
tinuous cross ties. The maximum length-to-width 
ratio of the structural subdiaphragm shall be 2~ to 
1. Connections and anchorages capable of resist- 
ing the prescribed forces shall be provided between 
the diaphragm and the attached components. Con- 
nections shall extend into the diaphragm a suffi- 
cient distance to develop the force transferred into 
the diaphragm. 

The strength design forces for steel elements of 
the wall anchorage system, other than anchor bolts 
and reinforcing steel, shall be 1.4 times the forces 
otherwise required by this Section. 

In wood diaphragms, the continuous ties shall 
be in addition to the diaphragm sheathing. Anchor- 
age shall not be accomplished by use of toe nails or 
nails subject to withdrawal nor shall wood ledgers 
of framing be used in cross-grain bending or cross- 
grain tension. The diaphragm sheathing shall not 
be considered effective as providing the ties or 
struts required by this Section. 

In metal deck diaphragms, the metal deck shall 
not be used as the continuous ties required by 
this Section in the direction perpendicular to the 
deck span. 

Diaphragm to wall anchorage using embedded 
straps shall be attached to, or hooked around, the 
reinforcing steel or otherwise terminated so as to 
effectively transfer forces to the reinforcing steel. 

When elements of the wall anchorage system 
are loaded eccentrically or are not perpendicular 
to the wall, the system shall be designed to 
resist all components of the forces induced by the 
eccentricity. 

When pilasters are present in the wall, the 
anchorage force at the pilasters shall be calculated 
considering the additional load transferred from 
the wall panels to the pilasters. However, the 
minimum anchorage force at a floor or roof shall 
not be reduced. 



0-&S DS IW p 



where 



(Eq. 9.5.2.63.2) 



F p = the design force in the individual anchors 
S DS — the design spectral response acceleration 
at short periods per Section 9.4.1.2.5 
/ = the occupancy importance factor per 
Section 9.1.4 



9.5.2.6.4 Seismic Design Category D. Structures 
assigned to Category D shall conform to the require- 
ments of Section 9.5.2.6.3 for Category C and to the 
requirements of this Section. 

9.5.2.6.4.1 Collector Elements. In addition to 
the requirements of Section 9.5.2.6.3.1, collector 
elements, splices, and their connections to resisting 



Minimum Design Loads for Buildings and Other Structures 



143 



elements shall resist the forces determined in 
accordance with Section 9.5.2.6.4.4. 

9.5.2.6.4.2 Plan or Vertical Irregularities. When 
the ratio of the strength provided in any story to 
the strength required is less than two-thirds of 
that ratio for the story immediately above, the 
potentially adverse effect shall be analyzed and 
the strengths shall be adjusted to compensate for 
this effect. 

For structures having a plan structural irreg- 
ularity of Type 1, 2, 3, or 4 in Table 9.5.2.3.2 
or a vertical structural irregularity of Type 4 in 
Table 9.5.2.3.3, the design forces determined from 
Section 9.5.5.2 shall be increased 25% for con- 
nections of diaphragms to vertical elements and 
to collectors and for connections of collectors to 
the vertical elements. Collectors and their connec- 
tions also shall be designed for these increased 
forces unless they are designed for the special seis- 
mic loads of Section 9.5.2.7.1, in accordance with 
Section 9.5.2.6.3.1. 

9.5.2.6.4.3 Vertical Seismic Forces. The vertical 
component of earthquake ground motion shall be 
considered in the design of horizontal cantilever 
and horizontal prestressed components. The load 
combinations used in evaluating such components 
shall include E as defined by Eqs. 9.5.2.7-1 and 
9.5.2.7-2. Horizontal cantilever structural compo- 
nents shall be designed for a minimum net upward 
force of 0.2 times the dead load in addition to the 
applicable load combinations of Section 9.5.2.7. 

9.5.2.6.4.4 Diaphragms. The deflection in the 
plane of the diaphragm shall not exceed the 
permissible deflection of the attached elements. 
Permissible deflection shall be that deflection that 
will permit the attached elements to maintain 
structural integrity under the individual loading 
and continue to support the prescribed loads. Floor 
and roof diaphragms shall be designed to resist 
design seismic forces determined in accordance 
with Eq. 9.5.2.6.4.4 as follows: 



The force determined from Eq. 9.5.2.6.4.4 need 
not exceed QASd$Iw px but shall not be less than 
O.lSosIWpx- When the diaphragm is required to 
transfer design seismic force from the vertical 
resisting elements above the diaphragm to other 
vertical resisting elements below the diaphragm 
due to offsets in the placement of the elements 
or to changes in relative lateral stiffness in the 
vertical elements, these forces shall be added to 
those determined from Eq. 9.5.2.6.4.4. 

9.5.2.6.5 Seismic Design Categories E and F. Struc- 
tures assigned to Seismic Design Categories E and F 
shall conform to the requirements of Section 9.5.2.6.4 
for Seismic Design Category D and to the require- 
ments of this Section. 

9.5.2.6.5.1 Plan or Vertical Irregularities. 
Structures having plan irregularity Type lb of 
Table 9.5.2.3.1 or vertical irregularities Type lb or 
5 of Table 9.5.2.3.3 shall not be permitted. 

9.5.2.7 Combination of Load Effects. The effects on 
the structure and its components due to seismic forces 
shall be combined with the effects of other loads in 
accordance with the combinations of load effects given 
in Section 2. For use with those combinations, the 
earthquake-induced force effect shall include vertical and 
horizontal effects as given by Eq. 9.5.2.7-1 or 9.5.2.7-2, 
as applicable. The vertical seismic effect term 0.2SdsF> 
need not be included where Sos is equal to or less 
than 0.125 in Eqs. 9.5.2.7-1, 9.5.2.7-2, 9.5.2.7.1-1, and 
9.5.2.7.1-2. The vertical seismic effect term 0.2SosE> 
need not be included in Eq. 9.5.2.7-2 when considering 
foundation overturning. 

for load combination 5 in Section 2.3.2 or load combi- 
nation 5 in Section 2.4.1: 



E = pQ E +0.2S DS D 



(Eq. 9.5.2.7-1) 



for load combination 7 in Section 2.3.2 or load combi- 
nation 8 in 2.4.1: 



E* 



j^ l—X 

F DX = — w 



where 



px ~ n wpx 

l=X 



(Eq. 9.5.2.6.4.4) 



£' 



F px = the diaphragm design force 
Fi = the design force applied to Level /" 
Wj — the weight tributary to Level / 

w px = the weight tributary to the diaphragm at 
Level x 



E = pQ E -0.2S DS D 



(Eq. 9.5.2.7-2) 



where 



E = the effect of horizontal and vertical 
earthquake-induced forces 
Sos = the design spectral response acceleration at 
short periods obtained from Section 9.4.1.2.5 
D — the effect of dead load, D 
Q E — the effect of horizontal seismic 
(earthquake-induced) forces 
p = the reliability factor 



144 



ASCE 7-02 



9.5.2.7.1 Special Seismic Load. Where specifically 
indicated in this Standard, the special seismic load 
of Eq. 9.5.2.7.1-1 shall be used to compute E for 
use in load combination 5 in Section 2.3.2 or load 
combination 3 in 2.4.1 and the special seismic load 
of Eq. 9.5.2.7.1-2 shall be used to compute E in load 
combination 7 in Section 2.3.2 or load combination 5 
in Section 2.4,1: 



E = Q Q E +Q2S DS D 
E = n o Q E -02S DS D 



(Eq. 9.5.2.7.14) 
(Eq. 9.5.2.7.1-2) 



The value of the quantity Q Qe in Eqs. 9.5.2.7.1- 
1 and 9.5.2.7.1-2 need not be taken greater than the 
capacity of other elements of the structure to transfer 
force to the component under consideration. 

Where allowable stress design methodologies are 
used with the special load of this Section applied in 
load combinations 3 or 5 of Section 2.4.1, allowable 
stresses are permitted to be determined using an 
allowable stress increase of 1.2. This increase shall 
not be combined with increases in allowable stresses 
or load combination reductions otherwise permitted 
by this standard or the material reference standard 
except that combination with the duration of load 
increases permitted in Ref. 9-12.1 is permitted. 

9.5.2,8 Deflection, Drift Limits, and Building Separa- 
tion. The design story drift (A) as determined in 
Section 9.5.5.7 or 9.5.6.6, shall not exceed the allowable 
story drift (A a ) as obtained from Table 9.5.2.8 for 
any story. For structures with significant torsional 
deflections, the maximum drift shall include torsional 
effects. All portions of the structure shall be designed 



and constructed to act as an integral unit in resisting 
seismic forces unless separated structurally by a 
distance sufficient to avoid damaging contact under total 
deflection (S x ) as determined in Section 9.5.5.7.1 

9.5.3 Index Force Analysis Procedure for Seismic 
Design of Buildings. See Section 9.5.2.5.1 for limitations 
on the use of this procedure. An index force analysis shall 
consist of the application of static lateral index forces to a 
linear mathematical model of the structure, independently 
in each of two orthogonal directions. The lateral index 
forces shall be as given by Eq. 9.5.3-1 and shall be applied 
simultaneously at each floor level. For purposes of analysis, 
the structure shall be considered to be fixed at the base: 



F x =0.01^ 



(Eq. 9.53-1) 



where 



F x = the design lateral force applied at story x 

w x — the portion of the total gravity load of the structure, 

W, located or assigned to Level x 
W — the effective seismic weight of the structure, 

including the total dead load and other loads 

listed below: 

1. In areas used for storage, a minimum of 25% of 
the floor live load (floor live load in public 
garages and open parking structures need not 

be included.) 

2. Where an allowance for partition load is 
included in the floor load design, the actual 
partition weight or a minimum weight of 10 psf 
(0.48 kN/m 2 ) of floor area, whichever is greater. 

3. Total operating weight of permanent equipment. 

4. 20% of flat roof snow load where flat roof snow 
load exceeds 30 psf (1.44 kN/m 2 ). 



TABLE 9.5.2.8 
ALLOWABLE STORY DRIFT, A a a 



Structure 


Seismic Use Group 


1 


Si 


esi 


Structures, other than masonry shear wall or masonry wall 
frame structures, four stories or less with interior walls, 
partitions, ceilings and exterior wall systems that have been 
designed to accommodate the story drifts. 


0.025/2,/ 


omoh sx 


Q.0\5h sx 


Masonry cantilever shear wall structures 


0.010/*, A . 


omoh sx 


0.010/z,, 


Other masonry shear wall structures 


0.001h sx 


0.001h sx 


0.007/i JJC 


Masonry wall frame structures 


0M3h sx 


0.013/*,* 


0.010/^, 


All other structures 


omoh 5X 


0.015/2, A - 


0.010/*,, 



a h sx is the story height below Level x. 

b There shall be no drift limit for single-story structures with interior walls, partitions, ceilings, and exterior wall systems that have been designed to 

accommodate the story drifts. The structure separation requirement of Section 9.5.2.8 is not waived. 

c Structures in which the basic structural system consists of masonry shear walls designed as vertical elements cantilevered from their base or foundation 

support which are so constructed that moment transfer between shear walls (coupling) is negligible. 



Minimum Design Loads for Buildings and Other Structures 



145 



9,5.4 Simplified Analysis Procedure for Seismic Design 
of Buildings. See Section 9.5.2.5.1 for limitations on the 
use of this procedure. For purposes of this analysis proce- 
dure, a building is considered to be fixed at the base. 

9.5.4.1 Seismic Base Shear. The seismic base shear, V, 
in a given direction shall be determined in accordance 
with the following formula: 



1.25, 



DS 



R 



W 



(Eq. 9.5.4.1) 



where 

Sds — 



the design elastic response acceleration at 

short period as determined in accordance 

with Section 9.4.1.2.5 
R = the response modification factor from 

Table 9.5.2.2 
W = the effective seismic weight of the structure 

as defined in Section 9.5.3 

9.5.4.2 Vertical Distribution. The forces at each level 
shall be calculated using the following formula: 



F x 



1.25 



DS 



R 



-W x 



(Eq. 9.5.4.2) 



where 



w x ~ the portion of the effective seismic weight of 
the structure, W, at level x 

9.5.4.3 Horizontal Distribution. Diaphragms construc- 
ted of wood structural panels or untopped steel decking 
are permitted to be considered as flexible. 

9.5.4.4 Design Drift. For the purposes of Section 
9.5.2.8, the design story drift, A, shall be taken as 1% of 
the story height unless a more exact analysis is provided. 

9.5.5 Equivalent Lateral Force Procedure. 

9.5.5.1 General. Section 9.5.5 provides required mini- 
mum standards for the equivalent lateral force procedure 
of seismic analysis of structures. An equivalent lateral 
force analysis shall consist of the application of equiva- 
lent static lateral forces to a linear mathematical model 
of the structure. The directions of application of lateral 
forces shall be as indicated in Section 9.5.2.5.2. The lat- 
eral forces applied in each direction shall be the total 
seismic base shear given by Section 9.5.5.2 and shall be 
distributed vertically in accordance with the provisions 
of Section 9.5.5.3. For purposes of analysis, the structure 
is considered to be fixed at the base. See Section 9.5.2.5 
for limitations on the use of this procedure. 



9.5.5.2 Seismic Base Shear. The seismic base shear 
(V) in a given direction shall be determined in 
accordance with the following equation: 



V = C S W 



(Eq. 9.5.5.2-1) 



where 



C s — the seismic response coefficient determined in 

accordance with Section 9.5.5.2.1 
W = the total dead load and applicable portions of 

other loads as indicated in Section 9.5.3 

9.5.5.2.1 Calculation of Seismic Response Coeffi- 
cient. When the fundamental period of the structure 
is computed, the seismic design coefficient (C s ) 
shall be determined in accordance with the 
following equation: 



C s - 



s 



DS 

rJi 



(Eq. 9.5.5.2.1-1) 



where 



S DS = tri e design spectral response acceleration in 
the short period range as determined from 
Section 9.4.1.2.5 
R — the response modification factor in 

Table 9.5.2.2 
/ = the occupancy importance factor determined 
in accordance with Section 9.1.4 

A soil-structure interaction reduction shall not 
be used unless Section 9.5.9 or another generally 
accepted procedure approved by the authority having 
jurisdiction is used. 

Alternatively, the seismic response coefficient, 
(Cy), need not be greater than the following equation: 



C, = 



Sd\ 



T(R/I) 
but shall not be taken less than 

C s =0.044S DS I 



(Eq. 9.5.5.2.1-2) 



(Eq. 9.5.5.2.1-3) 



nor for buildings and structures in Seismic Design 
Categories E and F 



Qs 



0.5S { 
~R/T 



(Eq. 9.5.5.2.1-4) 



where / and R are as defined above and 

S D \ = the design spectral response acceleration at a 
period of 1.0 sec. in units of g-sec, as 
determined from Section 9.4.1.2.5 
T = the fundamental period of the structure (sec) 
determined in Section 9.5.5.3 



146 



ASCE 7-02 



S\ = the mapped maximum considered earthquake 
spectral response acceleration determined in 
accordance with Section 9.4.1 

A soil-structure interaction reduction is permitted 
when determined using Section 9.5.9. 

For regular structures 5 stories or less in height 
and having a period, 7\ of 0.5 sec or less, the 
seismic response coefficient, C s shall be permitted 
to be calculated using values of 1.5 g and 0.6 g, 
respectively, for the mapped maximum considered 
earthquake spectral response accelerations Ss and S\ . 

9.5.5.3 Period Determination. The fundamental period 
of the structure (T) in the direction under considera- 
tion shall be established using the structural properties 
and deformational characteristics of the resisting ele- 
ments in a properly substantiated analysis. The fun- 
damental period (T) shall not exceed the product of 
the coefficient for upper limit on calculated period (C M ) 
from Table 9.5.5.3 and the approximate fundamental 
period (T a ) determined from Eq. 9.5.5.3-1. As an alter- 
native to performing an analysis to determine the fun- 
damental period (T), it shall be permitted to use the 
approximate building period, (T a \ calculated in accor- 
dance with Section 9.5.5.3.2, directly. 

9.5.5.3.1 Upper Limit on Calculated Period. The 
fundamental building period (T) determined in a 
properly substantiated analysis shall not exceed the 
product of the coefficient for upper limit on calculated 
period (C u ) from Table 9.5.5.3.1 and the approximate 
fundamental period (T a ) determined in accordance 
with Section 9.5.5.3.2. 

9.5.5.3.2 Approximate Fundamental Period. The 
approximate fundamental period (7^), in seconds, 



TABLE 9.5.5.3.1 

COEFFICIENT FOR UPPER LIMST ON 

CALCULATED PERIOD 



Design Spectral Response 
Acceleration at 1 Second, S D1 


Coefficient C u 


>0.4 


1.4 


0.3 


1.4 


0.2 


1.5 


0.15 


1.6 


0.1 


1.7 


<0.05 


1.7 



shall be determined from the following equation: 

T a = C t h/ (Eq. 9.5.5.3.2-1) 

where h n is the height in ft above the base to the 
highest level of the structure and the coefficients C t 
and x are determined from Table 9.5.5.3.2. 

Alternatively, it shall be permitted to determine 
the approximate fundamental period (T a \ in seconds, 
from the following equation for structures not exceed- 
ing 12 stories in height in which the lateral-force- 
resisting system consists entirely of concrete or steel 
moment resisting frames and the story height is at 
least 10 ft (3 m): 



T a = 0AN 



(Eq. 9.5.5.3.2-la) 



where N = number of stories 

The approximate fundamental period, T a , in sec- 
onds for masonry or concrete shear wall struc- 
tures shall be permitted to be determined from 



TABLE 9.5.5.3.2 
VALUES OF APPROXIMATE PERIOD PARAMETERS C f AND x 



Structure Type 


c t 


X 


Moment resisting frame systems of steel in which the frames 
resist 100% of the required seismic force and are not enclosed 
or adjoined by more rigid components that will prevent the 
frames from deflecting when subjected to seismic forces 


0.028(0.068) a 


0.8 


Moment resisting frame systems of reinforced concrete in 
which the frames resist 100% of the required seismic force and 
are not enclosed or adjoined by more rigid components that 
will prevent the frame from deflecting when subjected to 
seismic forces 


0.016(0.044) a 


0.9 


Eccentrically braced steel frames 


0.03(0.07) a 


0.75 


AH other structural systems 


0.02(0.055) 


0.75 



— metric equivalents are shown in parentheses 



Minimum Design Loads for Buildings and Other Structures 



147 



Eq. 9.5.5.3.2-2 as follows: 
0.0019 



T 



h n 



(Eq. 9.5.5.3.2-2) 



where h n is as defined above and C w is calculated 
from Eq. 9.5.5.3.2-3 as follows: 



*-££(£) 



Ai 






1+0.83| 




)] 



(Eq. 9.5.5.3.2-3) 



where 



A B = the base area of the structure ft 2 
Ai = the area of shear wall "f ' in ft 2 
Di = the length of shear wall "/" in ft 
n = the number of shear walls in the building 

effective in resisting lateral forces in the 

direction under consideration 



9.5.5.4 Vertical Distribution of Seismic Forces. The 
lateral seismic force (F x ) (kip or kN) induced at any 
level shall be determined from the following equations: 



F — C V 

1 X ~~ ^vx y 



and 



C — 

K ~^ vx — 



WxK 



(Eq. 9.5.5.4-1) 



(Eq. 9.5.5.4-2) 



!>*? 



where 



C vx = vertical distribution factor 
V = total design lateral force or shear at 

the base of the structure, (kip or kN) 
W[ and w x = the portion of the total gravity load of 

the structure (W) located or assigned 

to Level / or x 
h( and h x = the height (ft or m) from the base to 

Level / or x 
k = an exponent related to the structure 

period as follows: 

for structures having a period of 

0.5 sec or less, k — 1 

for structures having a period of 

2.5 sec or more, k = 2 

for structures having a period between 

0.5 and 2.5 seconds, k shall be 2 or 

shall be determined by linear 

interpolation between 1 and 2 

9.5.5.5 Horizontal Shear Distribution and Torsion. 
The seismic design story shear in any story (V x ) (kip or 



kN) shall be determined from the following equation: 
\' x = YJ ft (Eq- 9.5.5.5) 

i—x 

where F z = the portion of the seismic base shear (V) 
(kip or kN) induced at Level i. 

9.5.5.5.1 Direct Shear. The seismic design story 
shear (V x ) (kip or kN) shall be distributed to the var- 
ious vertical elements of the seismic force-resisting 
system in the story under consideration based on the 
relative lateral stiffness of the vertical resisting ele- 
ments and the diaphragm. 

9.5.5.5.2 Torsion. Where diaphragms are not flexi- 
ble, the design shall include the torsional moment 
(M t ) (kip or kN) resulting from the location of 
the structure masses plus the accidental torsional 
moments (M ta ) (kip or kN) caused by assumed dis- 
placement of the mass each way from its actual 
location by a distance equal to 5% of the dimen- 
sion of the structure perpendicular to the direction 
of the applied forces. Where earthquake forces are 
applied concurrently in two orthogonal directions, the 
required 5% displacement of the center of mass need 
not be applied in both of the orthogonal directions at 
the same time, but shall be applied in the direction 
that produces the greater effect. 

Structures of Seismic Design Categories C, D, 
E, and F, where Type 1 torsional irregularity exists 
as defined in Table 9.5.2.3.2, shall have the effects 
accounted for by multiplying M ta at each level by a 
torsional amplification factor (A x ) determined from 
the following equation: 



(Eq. 9.5.5.5.2) 



1.25,v, 



where 

S max = the maximum displacement at Level x (in. 
or mm) 

the average of the displacements at the 
extreme points of the structure at Level x 
(in. or mm) 



J avg 



Exception: The torsional and accidental torsional 
moment need not be amplified for structures of 
light-frame construction. 

The torsional amplification factor (A x ) is not 
required to exceed 3.0. The more severe loading for 
each element shall be considered for design. 

9.5.5.6 Overturning. The structure shall be designed 
to resist overturning effects caused by the seismic 



148 



ASCE 7-02 



forces determined in Section 9.5.4.4. At any story, the 
increment of overturning moment in the story under 
consideration shall be distributed to the various vertical 
elements of the lateral force-resisting system in the same 
proportion as the distribution of the horizontal shears to 
those elements. 

The overturning moments at Level x (M x ) (kip-ft or 
kN-m) shall be determined from the following equation: 



M x 



Y,Fi(hi-h x ) (Eq. 9.5.5.6) 



where 



Ft = the portion of the seismic base 
shear (V) induced at Level i 
hi and h x = the height (in ft or m) from the base to 
Level i or x 

The foundations of structures, except inverted 
pendulum- type structures, shall be permitted to be 
designed for 75% of the foundation overturning design 
moment (Mf) (kip-ft or kN-m) at the foundation -soil 
interface determined using the equation for the 
overturning moment at Level x (M x ) (kip-ft or kN-m). 

9.5.5.7 Drift Determination and I* -Delta Effects. 
Story drifts and, where required, member forces and 
moments due to P -delta effects shall be determined in 
accordance with this Section. Determination of story 
drifts shall be based on the application of the design 
seismic forces to a mathematical model of the physical 
structure. The model shall include the stiffness and 
strength of all elements that are significant to the 
distribution of forces and deformations in the structure 
and shall represent the spatial distribution of the mass 
and stiffness of the structure. In addition, the model shall 
comply with the following: 

1. Stiffness properties of reinforced concrete and 
masonry elements shall consider the effects of 
cracked sections, and 

2. For steel moment resisting frame systems, the 
contribution of panel zone deformations to overall 
story drift shall be included. 

9.5.5.7.1 Story Drift Determination. The design 
story drift (A) shall be computed as the difference 
of the deflections at the top and bottom of the story 
under consideration. Where allowable stress design 
is used, A shall be computed using code- specified 
earthquake forces without reduction. 

Exception: For structures of Seismic Design Cat- 
egories C, D, E, and F having plan irregularity 
Types la or lb of Table 9.5.2.3.2, the design story 
drift, D, shall be computed as the largest difference 



of the deflections along any of the edges of the 
structure at the top and bottom of the story under 
consideration. 

The deflections of Level x at the center of the 
mass (8 X ) (in. or mm) shall be determined in accor- 
dance with the following equation: 



«* = 



Cd?>xe 



(Eq. 9.5.5.7.1) 



where 



Cd = the deflection amplification factor in 

Table 9.5.2.2 
S X€ = the deflections determined by an 

elastic analysis 
/ = the importance factor determined in 

accordance with Section 9.1.4 

The elastic analysis of the seismic force-resisting 
system shall be made using the prescribed seismic 
design forces of Section 9.5.5.4. For the purpose of 
this Section, the value of the base shear, V, used 
in Eq. 9.5.5.2-1 need not be limited by the value 
obtained from Eq. 9.5.5.2.1-3. 

For determining compliance with the story drift 
limitation of Section 9.5.2.8, the deflections at the 
center of mass of Level x (8 X ) (in. or mm) shall be 
calculated as required in this Section. For the purposes 
of this drift analysis only, the upper-bound limitation 
specified in Section 9.5.5.3 on the computed funda- 
mental period, 7\ in seconds, of the building does not 
apply for computing forces and displacements. 

Where applicable, the design story drift (A) (in. 
or mm) shall be increased by the incremental factor 
relating to the P -delta effects as determined in 
Section 9.5.5.7.2. 

When calculating drift, the redundancy coefficient, 
p, is not used. 

9.5.5.7.2 P -Delta Effects. P-delta effects on story 
shears and moments, the resulting member forces 
and moments, and the story drifts induced by these 
effects are not required to be considered when the sta- 
bility coefficient (0) as determined by the following 
equation is equal to or less than 0.10: 



V x h sx C d 



(Eq. 9.5.5.7.2-1.) 



where 



p x = the total vertical design load at and above 

Level x. (kip or kN); when computing P x , no 
individual load factor need exceed 1.0 

A = the design story drift as defined in 

Section 9.5.3.7.1 occurring simultaneously 
with V Xi (in. or mm) 



Minimum Design Loads for Buildings and Other Structures 



149 



V x = the seismic shear force acting between 

Levels x and x — 1 , (kip or kN) 
k sx = the story height below Level x, (in. or mm) 

Q = the deflection amplification factor in 
Table 9.5.2.2 

The stability coefficient (9) shall not exceed 9 fm 
determined as follows: 



%mx = ^zr < 0.25 



pc d 



(Eq. 9.5.5.7.2-2) 



where ft is the ratio of shear demand to shear capacity 
for the story between Level x and x — 1. This ratio 
may be conservatively taken as 1.0. 

When the stability coefficient (9) is greater than 
0.10 but less than or equal to mca , the incremental 
factor related to P -delta effects (cid) shall be deter- 
mined by rational analysis. To obtain the story drift 
for including the P -delta effect, the design story drift 
determined in Section 9.5.5.7.1 shall be multiplied by 
1.0/(1-0). 



When 9 is greater than 9 m 



the structure is 



potentially unstable and shall be redesigned. 

When the P -delta effect is included in an auto- 
mated analysis, Eq. 9.5.5.7.2-2 must still be satisfied, 
however, the value of 9 computed from Eq. 9.5.5.7.2- 
1 using the results of the P-delta analysis may be 
divided by (1 + 9) before checking Eq. 9.5.5.7.2-2. 

9,5.6 Modal Analysis Procedure, 

9.5.6.1 General Section 9.5.6 provides required stan- 
dards for the modal analysis procedure of seismic analy- 
sis of structures. See Section 9,5.2.5 for requirements for 
use of this procedure. The symbols used in this method 
of analysis have the same meaning as those for sim- 
ilar terms used in Section 9.5.3, with the subscript in 
denoting quantities in the m th mode. 

9.5.6.2 Modeling. A mathematical model of the struc- 
ture shall be constructed that represents the spatial dis- 
tribution of mass and stiffness throughout the structure. 

For regular structures with independent orthogo- 
nal seismic force-resisting systems, independent two- 
dimensional models are permitted to be constructed to 
represent each system. For irregular structures or struc- 
tures without independent orthogonal systems, a three- 
dimensional model incorporating a minimum of three 
dynamic degrees of freedom consisting of translation 
in two orthogonal plan directions and torsional rotation 
about the vertical axis shall be included at each level 
of the structure. Where the diaphragms are not rigid 
compared to the vertical elements of the lateral force- 
resisting system, the model should include representa- 
tion of the diaphragm's flexibility and such additional 
dynamic degrees of freedom as are required to account 



for the participation of the diaphragm in the structure's 
dynamic response. In addition, the model shall comply 
with the following; 

1. Stiffness properties of concrete and masonry 
elements shall consider the effects of cracked 
sections, and 

2. For steel moment frame systems, the contribution 
of panel zone deformations to overall story drift 
shall be included. 

9.5.6.3 Modes. An analysis shall be conducted to deter- 
mine the natural modes of vibration for the structure, 
including the period of each mode, the modal shape vec- 
tor O, the modal participation factor, and modal mass. 
The analysis shall include a sufficient number of modes 
to obtain a combined modal mass participation of at 
least 90% of the actual mass in each of two orthogo- 
nal directions. 

9.5.6.4 Periods. The required periods, mode shapes, 
and participation factors of the structure in the direction 
under consideration shall be calculated by established 
methods of structural analysis for the fixed-base con- 
dition using the masses and elastic stiffnesses of the 
seismic force-resisting system. 

9.5.6.5 Modal Base Shear. The portion of the base 
shear contributed by the m th mode (V m ) shall be deter- 
mined from the following equations: 



(Eq. 9.5.6.5-1) 




(Eq. 9.5.6.5-2) 



where 



i=i. 



C sm = the modal seismic design coefficient 

determined below 
W m = the effective modal gravity load 
Wj — the portion of the total gravity load of the 

structure at Level / 
4> im ~ the displacement amplitude at the z' th level of 

the structure when vibrating in its m th mode 

The modal seismic design coefficient (C sm ) shall be 
determined in accordance with the following equation: 



C 



where 



R/I 



(Eq. 9.5.6.5-3) 



S am = the design spectral response acceleration at 
period T m determined from either the general 
design response spectrum of Section 9.4.1.2.6 
or a site-specific response spectrum per 
Section 9.4.1.3 



150 



ASCE 7-02 



R — the response modification factor determined 

from Table 9.5.2.2 
/ — the occupancy importance factor determined 
in accordance with Section 9.1.4 
T m = the modal period of vibration (in seconds) of 
the m ih mode of the structure 

Exception: When the general design response spec- 
trum of Section 9.4.1.2.6 is used for structures where 
any modal period of vibration (T m ) exceeds 4.0 sec, 
the modal seismic design coefficient (C sm ) for that 
mode shall be determined by the following equation: 



C Sl 



45, 



D\ 



wnT> 



(Eq. 9.5.6.5-4) 



The reduction due to soil-structure interaction as 
determined in Section 9.5.5.3 is permitted to be used. 

9.5.6.6 Modal Forces, Deflections, and Drifts. The 
modal force (F xm ) at each level shall be determined by 
the following equations: 



F ~~ C V 

1 xm — ^vxm v m 



and 






yj x (p x 






(Eq. 9.5.6.6-1) 



(Eq. 9.5.6.6-2) 



where 



C vxm = the vertical distribution factor in the 
m th mode 
V m = the total design lateral force or shear 
at the base in the m th mode 
Wi and xv x — the portion of the total gravity load of 
the structure (W) located or assigned 
to Level i or x 
(j) xm = the displacement amplitude at the x th 
level of the structure when vibrating 
in its m th mode 
4> im = the displacement amplitude at the / th 
level of the structure when vibrating 
in its m th mode 

The modal deflection at each level (8 xm ) shall be 
determined by the following equations: 



Sxn 



Cd&xe 



and 



5 - = (■£?) ( 



T 2 F 

1 m l xm 



W x 



(Eq. 9.5.6.6-3) 



(Eq. 9.5.6.6-4) 



where 

Cd — the deflection amplification factor determined 
from Table 9.5.2.2 
8 xem — the deflection of Level x in the m th mode at 
the center of the mass at Level x determined 
by an elastic analysis 
g = the acceleration due to gravity (ft 2 /sec) 
/ = the occupancy importance factor determined 
in accordance with Section 9.1.4 
T m = the modal period of vibration, in seconds, of 

the m ih mode of the structure 
F X m — the portion of the seismic base shear in the 

m th mode, induced at Level x, and 
w x = the portion of the total gravity load of the 
structure (W) located or assigned to Level x 

The modal drift in a story (A,„) shall be computed 
as the difference of the deflections (8 xm ) at the top and 
bottom of the story under consideration. 



9.5.6.7 Modal Story Shears and Moments. The story 
shears, story overturning moments, and the shear forces 
and overturning moments in vertical elements of the 
structural system at each level due to the seismic 
forces determined from the appropriate equation in 
Section 9.5.6.6 shall be computed for each mode by 
linear static methods. 



9.5.6.8 Design Values. The design value for the modal 
base shear (V f ), each of the story shear, moment and 
drift quantities, and the deflection at each level shall be 
determined by combining their modal values as obtained 
from Sections 9.5.6.6 and 9.5.6.7. The combination shall 
be carried out by taking the square root of the sum of 
the squares of each of the modal values or where closely 
spaced periods in the translational and torsional modes 
result in significant cross-correlation of the modes, 
the complete quadratic combination (CQC) method, in 
accordance with ASCE-4, shall be used. 

A base shear (V) shall be calculated using the equiv- 
alent lateral force procedure in Section 9.5.5. For the 
purpose of this calculation, a fundamental period of the 
structure (T), in seconds, shall not exceed the coefficient 
for upper limit on the calculated period (C u ) times the 
approximate fundamental period of the structure (T a ). 
Where the design value for the modal base shear (V t ) 
is less than 85% of the calculated base shear (V) using 
the equivalent lateral force procedure, the design story 
shears, moments, drifts, and floor deflections shall be 
multiplied by the following modification factor: 



0.85- 



Vt 



(Eq. 9.5.6.8) 



Minimum Design Loads for BuiSdings and Other Structures 



151 



where 

V — the equivalent lateral force procedure base 
shear, calculated in accordance with this 
section and Section 9.5.5, and 

V t = the modal base shear, calculated in accordance 
with this section 

9.5,6.9 Horizontal Shear Distribution. The distribu- 
tion of horizontal shear shall be in accordance with the 
requirements of Section 9.5.5.5 except that amplification 
of torsion per Section 9.5.5.5.2 is not required for that 
portion of the torsion, A x , included in the dynamic anal- 
ysis model. 

.9.5,6.10 Foundation Overturning. The foundation 
overturning moment at the foundation-soil interface may 
be reduced by 10%. 

9.5.6.11 P -Delta Effects. The P-delta effects shall be 
determined in accordance with Section 9.5.5.7. The story 
drifts and base shear used to determine the story shears 
shall be determined in accordance with Section 9.5.5.7.1. 

9.5.7 Linear Response History Analysis Procedure. A 
linear response history analysis shall consist of an analysis 
of a linear mathematical model of the structure to determine 
its response, through methods of numerical integration, to 
suites of ground motion acceleration histories compatible 
with the design response spectrum for the site. The analysis 
shall be performed in accordance with the provisions 
of this Section. For purposes of analysis, the structure 
shall be permitted to be considered to be fixed at the 
base, or alternatively, it shall be permitted to use realistic 
assumptions with regard to the stiffness of foundations. See 
Section 9.5.2.1 for limitations on the use of this procedure. 

9.5.7.1 Modeling. Mathematical models shall conform 
to the requirements of Section 9.5.6. 1. 

9.5.7.2 Ground Motion. A suite of not less than three 
appropriate ground motions shall be used in the analysis. 
Ground motion shall conform to the requirements of 
this Section. 

9.5.7.2.1 Two-Dimensiona! Analysis. When two- 
dimensional analyses are performed, each ground 
motion shall consist of a horizontal acceleration his- 
tory, selected from an actual recorded event. Appro- 
priate acceleration histories shall be obtained from 
records of events having magnitudes, fault distance, 
and source mechanisms that are consistent with those 
that control the maximum considered earthquake. 
Where the required number of appropriate recorded 



ground motion records are not available, appropri- 
ate simulated ground motion records shall be used 
to make up the total number required. The ground 
motions shall be scaled such that the average value 
of the 5% damped response spectra for the suite 
of motions is not less than the design response 
spectrum for the site, determined in accordance with 
Section 9.4.1.3 for periods ranging from 0.27 to 
1.5T sec where T is the natural period of the structure 
in the fundamental mode for the direction of response 
being analyzed. 

9.5.7.2.2 Tiiree-Dimensiona! Analysis. When three- 
dimensional analyses are performed, ground motions 
shall consist of pairs of appropriate horizontal ground 
motion acceleration components that shall be selected 
and scaled from individual recorded events. Appro- 
priate ground motions shall be selected from events 
having magnitudes, fault distance, and source mech- 
anisms that are consistent with those that control the 
maximum considered earthquake. Where the required 
number of recorded ground motion pairs are not avail- 
able, appropriate simulated ground motion pairs shall 
be used to make up the total number required. For 
each pair of horizontal ground motion components, 
the square root of the sum of the squares (SRSS) of 
the 5% damped response spectrum of the scaled hor- 
izontal components shall be constructed. Each pair 
of motions shall be scaled such that the average 
value of the SRSS spectra from all horizontal compo- 
nent pairs is not less than 1.3 times the 5% damped 
design response spectrum determined in accordance 
with Section 9.4.1.3 for periods ranging from 0.2T 
to 1.5T seconds, where T is the natural period of the 
fundamental mode of the structure. 

9.5.7.3 Response Parameters. For each ground motion 
analyzed, the individual response parameters shall be 
scaled by the quantity I/R, where I is the occu- 
pancy importance factor determined in accordance with 
Section 1.4 and R is the Response Modification Coef- 
ficient selected in accordance with Section 9.5.2.2. The 
maximum value of the base shear, V,, member forces, 
Qei, and interstory drifts, d[ at each story, scaled as 
indicated above shall be determined. When the maxi- 
mum scaled base shear predicted by the analysis, V/, is 
less than given by Eq. 9.5.5.1.2-3, or in Seismic Design 
Categories E and F, Eq. 9.5.5.1.2-4, the scaled member 
forces, Q ei , shall be additionally scaled by the factor: 



V 



(Eq. 9.5.7.3) 



where V is the minimum base shear determined in 
accordance with Eq. 9.5.5.2.1-3 or for structures in 
Seismic Design Category E or F, Eq. 9.5.5.2.1-4. 



152 



ASCE 7-02 



If at least seven ground motions are analyzed, the 
design member forces, Q E , used in the load combina- 
tions of Section 9.5.2.7, and the design interstory drift, 
D, used in the evaluation of drift in accordance with 
Section 5.2.8 shall be permitted to be taken respectively 
as the average of the scaled Qe\ and D[ values deter- 
mined from the analyses and scaled as indicated above. If 
less than seven ground motions are analyzed, the design 
member forces, Q E , and the design interstory drift, D y 
shall be taken as the maximum value of the scaled Q E t 
and Di values determined from the analyses. 

Where these provisions require the consideration of 
the special load combinations of Section 9.5.2.7, the 
value of QqQe need not be taken larger than the 
maximum of the unsealed value, Qei, obtained from 
the suite of analyses. 

9.5.8 Nonlinear Response History Analysis. A nonlinear 
response history analysis shall consist of an analysis of a 
mathematical model of the structure that directly accounts 
for the nonlinear hysteretic behavior of the structure's 
components to determine its response through methods of 
numerical integration to suites of ground motion accelera- 
tion histories compatible with the design response spectrum 
for the site. The analysis shall be performed in accordance 
with this Section. See Section 9.5.2.1 for limitations on the 
use of this procedure. 

9.5.8.1 Modeling. A mathematical model of the struc- 
ture shall be constructed that represents the spatial distri- 
bution of mass throughout the structure. The hysteretic 
behavior of elements shall be modeled consistent with 
suitable laboratory test data and shall account for all sig- 
nificant yielding, strength degradation, stiffness degrada- 
tion, and hysteretic pinching indicated by such test data. 
Strength of elements shall be based on expected val- 
ues considering material overstrength, strain hardening, 
and also hysteretic strength degradation. Linear proper- 
ties, consistent with the provisions of Section 9.5.6.1, 
shall be permitted to be used for those elements demon- 
strated by the analysis to remain within their linear range 
of response. The structure shall be assumed to have a 
fixed base, or alternatively, it shall be permitted to use 
realistic assumptions with regard to the stiffness and 
load-carrying characteristics of the foundations consis- 
tent with site-specific soils data and rational principles 
of engineering mechanics. 

For regular structures with independent orthogo- 
nal seismic force-resisting systems, independent two- 
dimensional models shall be permitted to be constructed 
to represent each system. For structures having plan 
irregularities Types la, lb, 4 or 5 of Table 9.5.2.3.2, 
or structures without independent orthogonal systems, 
a three-dimensional model incorporating a minimum of 
three dynamic degrees of freedom consisting of trans- 
lation in two orthogonal plan directions and torsional 



rotation about the vertical axis at each level of the struc- 
ture shall be used, Where the diaphragms are not rigid 
compared to the vertical elements of the lateral -force- 
resisting system, the model should include representa- 
tion of the diaphragm's flexibility and such additional 
dynamic degrees of freedom as are required to account 
for the participation of the diaphragm in the structure's 
dynamic response. 

9.5.8.2 Ground Motion and Other Loading. Ground 
motion shall conform to the provisions of Section 9.5.7.2. 
The structure shall be analyzed for the effects of these 
ground motions simultaneously with the effects of dead 
load in combination with not less than 25% of the required 
live loads. 

9.5.8.3 Response Parameters. For each ground motion 
analyzed, individual response parameters consisting of 
the maximum value of the individual member forces, 
Qei, member inelastic deformations, D, and interstory 
drifts, Di at each story shall be determined. 

If at least seven ground motions are analyzed, the 
design values of member forces, Q E , member inelastic 
deformations, D and interstory drift, D shall be permit- 
ted to be taken respectively as the average of the scaled 
Qei, gi, and D, values determined from the analyses. If 
less than seven ground motions are analyzed, the design 
member forces, Q E , design member inelastic deforma- 
tions, g and the design interstory drift, L>, shall be taken 
as the maximum value of the scaled Q Ei , g/, and De- 
values determined from the analyses. 

9.5.83.1 Member Strength. The adequacy of mem- 
bers to resist the combination of load effects of 
Section 9.5.2.7 need not be evaluated. 

Exception: Where this Standard requires the 
consideration of the special seismic loads of 
Section 9.5.2.7.1. In such evaluations, the max- 
imum value of Qei obtained from the suite of 
analyses shall be taken in place of the quantity 
tt Q E . 

9.5.83.2 Member Deformation. The adequacy of 
individual members and their connections to with- 
stand the estimated design deformation values, g ( , as 
predicted by the analyses shall be evaluated based 
on laboratory test data for similar components. The 
effects of gravity and other loads on member deforma- 
tion capacity shall be considered in these evaluations. 
Member deformation shall not exceed two-thirds of 
a value that results in loss of ability to carry grav- 
ity loads or that results in deterioration of member 
strength to less than the 67% of the peak value. 



Minimum Design Loads for Buildings and Other Structures 



153 



9.5.833 Interstory Drift. The design interstory drift 
obtained from the analyses shall not exceed 125% of 
the drift limit specified in Section 9.5.2.8. 

9.5.8,4 Design Review, A design review of the seismic 
force-resisting system and the structural analysis shall 
be performed by an independent team of registered 
design professionals in the appropriate disciplines and 
others experienced in seismic analysis methods and the 
theory and application of nonlinear seismic analysis 
and structural behavior under extreme cyclic loads. The 
design review shall include, but not be limited to, 
the following: 

1. Review of any site-specific seismic criteria 
employed in the analysis including the develop- 
ment of site- specific spectra and ground motion 
time histories 

2. Review of acceptance criteria used to demonstrate 
the adequacy of structural elements and systems 
to withstand the calculated force and deformation 
demands, together with that laboratory and other 
data used to substantiate these criteria. 

3. Review of the preliminary design including the 
selection of structural system and the configuration 
of structural elements. 

4. Review of the final design of the entire structural 
system and all supporting analyses. 

9.5.9 Soil-Structure Interaction, 

9.5.9.1 General. If the option to incorporate the effects 
of soil-structure interaction is exercised, the require- 
ments of this Section shall be used in the determination 
of the design earthquake forces and the corresponding 
displacements of the structure. The use of these provi- 
sions will decrease the design values of the base shear, 
lateral forces, and overturning moments but may increase 
the computed values of the lateral displacements and the 
secondary forces associated with the P-delta effects. 

The provisions for use with the equivalent lateral 
force procedure are given in Section 9.5.9.2. and those 
for use with the modal analysis procedure are given in 
Section 9.5.9.3. 

9.5.9.2 Equivalent Lateral Force Procedure. The fol- 
lowing requirements are supplementary to those pre- 
sented in Section 9.5.5. 

9.5.9.2.1 Base Shear. To account for the effects of 
soil-structure interaction, the base shear (V) deter- 
mined from shall be reduced to: 



The reduction (A V) shall be computed as follows and 
shall not exceed 0.3 V: 



AV ' = 



c _ r 



0.05 
B 



0.4" 



W <03V 

(Eq. 9.5.9.2.1-2) 



where 



C s = the seismic design coefficient computed from 
Eqs. 9.5.5.2.1-1 and 9,5.5.2.1-2 using the 
fundamental natural period of the fixed-base 
structure (T or T a ) as specified in 
Section 9.5.3.3 

C s — the value of C s computed from 

Eqs. 9.5.5.2.1-1 and 9.5.5.2.1-2 using the 
fundamental natural period of the flexibly 
supported structure (T) defined in 
Section 9.5.5.2.1.1 

B — the fraction of critical damping for the 
structure-foundation system determined in 
Section 9.5.5.2.1.2, and 

W = the effective gravity load of the structure, 

which shall be taken as 0.7W, except that for 
structures where the gravity load is 
concentrated at a single level, it shall be taken 
equal to W 

9.5.9.2.1.1 Effective Building Period. The effec- 
tive period (T) shall be determined as follows: 



T = T 



N 



k 



i + 



Kyh 2 " 



K e J 
(Eq. 9.5.9.2.1.14) 



where 



T — the fundamental period of the 

structure as determined in 

Section 9.5.5.3 
k — the stiffness of the structure when 

fixed at the base, defined by the 

following: 



k = 4n 2 



W 



(Eq. 9.5.9.2.1.1-2) 



V = V - AV 



(Eq. 9.5.9.2.1-1) 



h — the effective height of the structure which 
shall be taken as 0.7 times the total 
height (h n ) except that for structure where 
the gravity load is effectively concentrated 
at a single level, it shall be taken 
as the height to that level 



154 



ASCE 7-02 



Ky = the lateral stiffness of the foundation 
defined as the horizontal force at the 
level of the foundation necessary to 
produce a unit deflection at that level, the 
force and the deflection being measured 
in the direction in which the structure is 
analyzed 

Ko — the rocking stiffness of the foundation 
defined as the moment necessary to 
produce a unit average rotation of the 
foundation, the moment and rotation 
being measured in the direction in which 
the structure is analyzed, and 
g — the acceleration of gravity 

The foundation stiffnesses (K y and K$) shall 
be computed by established principles of foun- 
dation mechanics using soil properties that are 
compatible with the soil strain levels associated 
with the design earthquake motion. The aver- 
age shear modulus (G) for the soils beneath 
the foundation at large strain levels and the 
associated shear wave velocity (v s ) needed in 
these computations shall be determined from 
Table 9.5.9.2.1.1a where 

v so = the average shear wave velocity for the 

soils beneath the foundation at small strain 

levels (10~ 3 % or less) 
G — yv^ /g — the average shear modulus for 

the soils beneath the foundation at small 

strain levels 
y = the average unit weight of the soils 

Alternatively, for structures supported on mat 
foundations that rest at or near the ground surface 
or are embedded in such a way that the side wall 
contact with the soil are not considered to remain 
effective during the design ground motion, the 
effective period of the structure is permitted to be 
determined from: 



T = T 



M 



1 + 



25a r a h 



1 + 



\.\2rji 



^3 



a 9 r~; / 
(Eq. 9.5.9.2.1.1-3) 



TABLE 9.5.9.2.1.1a 
VALUES OF G/G AND v s /v so 





Spectral Response Acceleration, S D1 


<0.10 


<0.15 


<0.20 


>0.30 


Value of G/G, 


0.81 


0.64 


0.49 


0.42 


Value of vjv s0 


0.9 


0.8 


0.7 


0.65 



TABLE 9.5.9.2.1. 1b 
VALUES OF O0 



r m /v s T 


a e 


<0.05 


1.0 


0.15 


0.85 


0.35 


0.7 


0.5 


0.6 



where 

a = the relative weight density of the structure 
and the soil defined by 



W 



a — 



yA h 



(Eq. 9.5.9.2.1.1-4) 



r a and r m = characteristic foundation lengths 
defined by 



and 



t~m — 



4/4/, 



(Eq. 9.5.9.2.1.1-5) 



(Eq. 9.5.9.2.1.1-6) 



where 

A ■■= the area of the load-carrying foundation 
I = the static moment of inertia of the 

load-carrying foundation about a horizontal 
centroidal axis normal to the direction in 
which the structure is analyzed 
a 9 = dynamic foundation stiffness modifier 
for rocking as determined from 
Table 9.5.9.2.1.1b 

where 

r m — characteristic foundation length as deter- 
mined by Eq. 9.5.9.2.1.1-6 

v s = shear wave velocity 

T = fundamental period as determined in 
Section 9.5.5.3 



9.5.9.2.1.2 Effective Damping. The effective 
damping factor for the structure-foundation system 
J3 shall be computed as follows: 



j8 = A, + 



0.05 



(Eq. 9.5.9.2.1.2-1) 



where 



fi — the foundation damping factor as specified 
in Figure 9.5.9.2.1.2 



Minimum Design Loads for Buildings and Other Structures 



155 



0.25 



0.20 - 



0.15 



Q. 

£ 
o 



o 0.10 - 



"D 



0.05 




1.4 1.6 
f/Tor f,/^ 



stiffer, rock-like deposit with an abrupt increase 
in stiffness, the factor O in Eq. 9.5.9.2.1.2-1 
shall be replaced by fi ( if 4D s /v s T < 1 where 
D s is the total depth of the stratum. fi f shall be 
determined as follows: 






(Eq. 9.5.9.2X2-4) 



The value of ft computed from Eq. 9.5.9.2.1.2- 
1, both with or without the adjustment 
represented by Eq. 9.5.9.2.1.2-4, shall in no 
case be taken as less than ft = 0.05 or greater 
than J3 = 0.20. 

9.5.9.2.2 Vertical Distribution of Seismic Forces. 
The distribution over the height of the structure of the 
reduced total seismic force (V) shall be considered to 
be the same as for the structure without interaction. 



FIGURE 9.5.9.2.1.2 
FOUNDATION DAMPING FACTOR 

The values of f$ corresponding to A v = 0.15 
in Figure 9.5.9.2.1.2 shall be determined by aver- 
aging the results obtained from the solid lines and 
the dashed lines. 

The quantity r in Figure 9.5.9.2.1.2 is a charac- 
teristic foundation length that shall be determined 
as follows: 

For h/L a < 0.5, 



r — r a 



' — (Eq. 9.5.9.2.1.2-2) 

71 



For h/L > 1, 



_ 4/ 41 

t — r m — -» / 

V 7T 



(Eq. 9.5.9.2,1.2-3) 



where 



L a — the overall length of the side of the foun- 
dation in the direction being analyzed 

A a — the area of the load-carrying foundation, 
and 

l — the static moment of inertia of the 

load-carrying foundation about a horizontal 
centroidal axis normal to the direction in 
which the structure is analyzed 

For intermediate values of h/L 09 the value of r 
shall be determined by linear interpolation. 

Exception: For structures supported on point 
bearing piles and in all other cases where the 
foundation soil consists of a soft stratum of rea- 
sonably uniform properties underlain by a much 



9.5,9,2.3 Other Effects. The modified story shears, 
overturning moments, and torsional effects about a 
vertical axis shall be determined as for structures 
without interaction using the reduced lateral forces. 

The modified deflections (l x ) shall be determined 
as follows: 



S x 



M h x 



+ S X 



(Eq. 9.5.9.2.3-1) 



where 



M — the overturning moment at the base 

determined in accordance with Section 9.5.3.6 
using the unmodified seismic forces and not 
including the reduction permitted in the design 
of the foundation 

h x = the height above the base to the level under 
consideration 

8 X = the deflections of the fixed-base structure as 
determined in Section 9.5.3.7.1 using the 
unmodified seismic forces 

The modified story drifts and P -delta effects shall 
be evaluated in accordance with the provisions of 
Section 9.5.3.7 using the modified story shears and 
deflections determined in this Section. 

9.5,9.3 Modal Analysis Procedure. The following pro- 
visions are supplementary to those presented in 
Section 9.5.6. 

9.5,9.3.1 Modal Base Shears, To account for the 
effects of soil -structure interaction, the base shear cor- 
responding to the fundamental mode of vibration (V\) 
shall be reduced to: 



V x = Vi - AVj 



156 



(Eq. 9.5.9.3.1-1) 
ASCE 7-02 



The reduction (AVi) shall be computed in accor- 
dance with Eq. 9.5,9.2.1-2 with W taken as equal 
to the gravity load W\ defined by Eq. 9.5.6.5-2, C s 
computed from Eq. 9.5.6.5-3 using the fundamen- 
tal period of the fixed-base structure (T\), and C s 
computed from Eq. 9.5.6.5-3 using the fundamental 
period of the elastically supported structure (T\). 

The period T\ shall be determined from 
Eq. 9.5.9.2.1.1-1, or from Eq. 9.5.9.2.1.1-3 when 

applicable, taking r_=fi, evaluating k from 

Eq. 9.5.9.2.1.1-2 with W = W U and computing h 
as follows: 



Yl Wl<pnhi 



h = ^ 






(Eq. 9.5.93.1-2) 



The above designated values of W, h, T, and 
f also shall be used to evaluate the factor 
a from Eq. 9.5.9.2.1.1-4 and factor /3 from 
Figure 9.5.9.2.1.2. No reduction shall be made in the 
shear components contributed by thejngher modes 
of vibration. The reduced base shear (V i) shall in no 
case be taken less than 0.7 Vi. 

9,5.93.2 Other Modal Effects, The modified modal 
seismic forces, story shears, and overturning moments 
shall be determined as for structure^ without 
interaction using the modified base shear (V instead 
of V\. The modified modal deflections (8) shall be 
determined as follows: 



Sxi - 



Vi 



l L 






+ &xi 



and 



(Eq. 9.5.93.24) 



(Eq. 9.5.93.2-2) 



for m — 2, 3, . . . 
where 

M \ = the overturning base moment for the 
fundamental mode of the fixed-base 
structure, as determined in Section 9.5.6.7 
using the unmodified modal base shear V\ 

S xm = the modal deflections at Level x of the 
fixed-base structure as determined in 
Section 9.5.6.6 using the unmodified modal 
shears, V m 

The modified modal drift in a story (A m ) shall be 
computed as the difference of the deflections (8 xm ) at 
the top and bottom of the story under consideration. 

9.5.933 Design Values. The design values of the 
modified shears, moments, deflections, and story 



drifts shall be determined as for structures without 
interaction by taking the square root of the sum of 
the squares of the respective modal contributions. In 
the design of the foundation, it shall be permitted to 
reduce the overturning moment at the foundation- soil 
interface determined in this manner by 10% as for 
structures without interaction. 

The effects of torsion about a vertical axis 
shall be evaluated in accordance with the provi- 
sions of Section 9.5.6.5 and the P-delta effects shall 
be evaluated in accordance with the provisions of 
Section 9.5.6.7.2 using the story shears and drifts 
determined in Section 9.5.9.3.2. 



SECTION 9-6 

ARCHITECTURAL, MECHANICAL, AND 

ELECTRICAL COMPONENTS AND SYSTEMS 

9.6.1 General. Section 9.6 establishes minimum design 
criteria for architectural, mechanical, electrical, and non- 
structural systems, components, and elements permanently 
attached to structures including supporting structures and 
attachments (hereinafter referred to as "components"). The 
design criteria establish minimum equivalent static force 
levels and relative displacement demands for the design of 
components and their attachments to the structure, recog- 
nizing ground motion and structural amplification, compo- 
nent toughness and weight, and performance expectations. 
Seismic Design Categories for structures are defined in 
Section 9.4.2. For the purposes of this Section, components 
shall be considered to have the same Seismic Design Cat- 
egory as that of the structure that they occupy or to which 
they are attached unless otherwise noted. 

This Section also establishes minimum seismic design 
force requirements for nonbuilding structures that are sup- 
ported by other structures where the weight of the nonbuild- 
ing structure is less than 25% of the combined weight of 
the nonbuilding structure and the supporting structure. Seis- 
mic design requirements for nonbuilding structures that are 
supported by other structures where the weight of the non- 
building structure is 25% or more of the combined weight 
of the nonbuilding structure and supporting structure are 
prescribed in Section 9.14. Seismic design requirements 
for nonbuilding structures that are supported at grade are 
prescribed in Section 9.14; however, the minimum seismic 
design forces for nonbuilding structures that are supported 
by another structure shall be determined in accordance 
with the requirements of Section 9.6.1.3 with R p equal to 
the value of R specified in Section 9.14 and a P = 2.5 for 
nonbuilding structures with flexible dynamic characteristics 
and a p = 1.0 for nonbuilding structures with rigid dynamic 
characteristics. The distribution of lateral forces for the sup- 
ported nonbuilding structure and all nonforce requirements 
specified in Section 9.14 shall apply to supported nonbuild- 
ing structures. 



Minimum Design Loads for Buildings and Other Structures 



157 



In addition, all components are assigned a component 
importance factor (I p ) in this chapter. The default value 
for I p is 1.00 for typical components in normal service. 
Higher values for I p are assigned for components, which 
contain hazardous substances, must have a higher level of 
assurance of function, or otherwise require additional atten- 
tion because of their life safety characteristics. Component 
importance factors are prescribed in Section 9.6.1.5. 

All architectural, mechanical, electrical, and other non- 
structural components in structures shall be designed and 
constructed to resist the equivalent static forces and dis- 
placements determined in accordance with this Section. The 
design and evaluation of support structures and architectural 
components and equipment shall consider their flexibility 
as well as their strength. 

Exception: The following components are exempt from 
the requirements of this Section: 

1. All components in Seismic Design Category A. 

2. Architectural components in Seismic Design Cat- 
egory B other than parapets supported by bearing 
walls or shear walls provided that the importance 
factor (I p ) is equal to 1.0. 

3. Mechanical and electrical components in Seismic 
Design Category B. 

4. Mechanical and electrical components in structures 
assigned to Seismic Design Category C provided 
that the importance factor (I p ) is equal to 1.0. 

5. Mechanical and electrical components in Seismic 
Design Categories D, E, and F where I p = 1.0 
and flexible connections between the components 
and associated ductwork, piping, and conduit are 
provided and that are mounted at 4 ft (1.22 m) or 
less above a floor level and weigh 400 lb (1780 N) 
or less. 

6. Mechanical and electrical components in Seismic 
Design Categories D, E, and F weighing 20 lb 
(95 N) or less where I p — 1.0 and flexible con- 
nections between the components and associated 
ductwork, piping, and conduit are provided, or 
for distribution systems, weighing 5 lb/ft (7 N/m) 
or less. 

The functional and physical interrelationship of com- 
ponents and their effect on each other shall be designed 
so that the failure of an essential or nonessential architec- 
tural, mechanical, or electrical component shall not cause 
the failure of a nearby essential architectural, mechanical, 
or electrical component. 

9,6.1.1 Reference Standards. 

9.6.1.1.1 Consensus Standards. The following ref- 
erences are consensus standards and are to be consid- 
ered part of these provisions to the extent referred to 
in this chapter: 



Reference 9.6-1 



Reference 9.6-2 



Reference 9.6-3 



Reference 9.6-4 



Reference 9.6-5 



Reference 9.6-6 



Reference 9.6-7 



Reference 9.6-8 



Reference 9.6-9 



Reference 9.6-10 



Reference 9.6-11 



Reference 9.6-12 



Reference 9.6-13 



American Society of Mechanical 
Engineers (ASME),ASMEA17.1 9 
Safety Code For Elevators and 
Escalators, 1996, 
American Society of Mechanical 
Engineers (ASME), Boiler And 
Pressure Vessel Code, including 
addendums through 1997. 
American Society For Testing 
and Materials (ASTM), ASTM 
C635, Standard Specification for 
the Manufacture, Performance, 
and Testing of Metal Suspension 
Systems For Acoustical Tile And 
Lay-in Panel Ceilings, 1997. 
American Society For Testing And 
Materials (ASTM), ASTM C636, 
Standard Practice for Installation 
of Metal Ceiling Suspension Sys- 
tems for Acoustical Tile And Lay- 
in Panels, 1996. 

American National Standards 
Institute/American Society of 
Mechanical Engineers, ASME 
B3 1.1-98, Power Piping. 
American Society of Mechanical 
Engineers, ASME B31.3-96, Pro- 
cess Piping. 

American Society of Mechani- 
cal Engineers, ASME B3 1.4-92, 
Liquid Transportation Systems for 
Hydrocarbons, Liquid Petroleum 
Gas, Anhydrous Ammonia, and 
Alcohols. 

American Society of Mechani- 
cal Engineers, ASME B31.5-92, 
Refrigeration Piping. 
American Society of Mechani- 
cal Engineers, ASME B31.9-96, 
Building Services Piping. 
American Society of Mechani- 
cal Engineers, ASME B 3 1. 11 -89 
(Reaffirmed 1998), Slurry Trans- 
portation Piping Systems. 
American Society of Mechani- 
cal Engineers, ASME B31.8-95, 
Gas Transmission and Distribu- 
tion Piping Systems. 
Institute of Electrical and Elec- 
tronic Engineers (IEEE), Standard 
344, Recommended Practice for 
Seismic Qualification of Class IE 
Equipment for Nuclear Power 
Generating Stations, 1987. 
National Fire Protection Associa- 
tion (NFPA), NFPA-13, Standard 



158 



ASCE 7-02 



for the Installation of Sprinkler 
Systems, 1999. 



9.6.1.1.2 Accepted Standards. The following refer- 
ences are standards developed within the industry and 
represent acceptable procedures for design and con- 
struction: 



Reference 9.6-14 



Reference 9.6-15 



Reference 9.6-16 



Reference 9.6-17 



Reference 9.6-18 



Reference 9.6-19 



Reference 9.6-20 



Reference 9.6-21 



American Society of Heating, 
Ventilating, and Air Condi- 
tioning (ASHRAE), "Seismic 
Restraint Design," 1999. 
Manufacturer' s Standardization 
Society of the Valve and Fit- 
ting Industry (MSS). SP-58, 
"Pipehangers and Supports — 
Materials, Design, and Manufac- 
ture;' 1988. 

Ceilings and Interior Systems 
Construction Association 

(CISCA), "Recommendations for 
Direct-Hung Acoustical Tile and 
Lay-in Panel Ceilings," Seismic 
Zones 0-2, 1991. 
Ceilings and Interior Systems 
Construction Association 

(CISCA), "Recommendations for 
Direct-Hung Acoustical Tile and 
Lay-in Panel Ceilings," Seismic 
Zones 3-4, 1991. 
Sheet Metal and Air Condition- 
ing Contractors National Asso- 
ciation (SMACNA.), HVACDuct 
Construction Standards, Metal 
and Flexible, 1995. 
Sheet Metal and Air Condition- 
ing Contractors National Asso- 
ciation (SMACNA), Rectangu- 
lar Industrial Duct Construction 
Standards, 1980. 
Sheet Metal and Air Con- 
ditioning Contractors National 
Association (SMACNA), Seis- 
mic Restraint Manual Guidelines 
for Mechanical Systems, 1991, 
including Appendix B, 1998. 
American Architectural Manu- 
facturers Association (A AM A), 
"Recommended Dynamic Test 
Method for Determining the 
Seismic Drift Causing Glass 
Fallout from a Wall System," 
Publication No. AAMA 501.6- 
2001. 



9.6.1.2 Component Force Transfer. Components shall 
be attached such that the component forces are trans- 
ferred to the structure. Component seismic attachments 
shall be bolted, welded, or otherwise positively fastened 
without consideration of frictional resistance produced 
by the effects of gravity. A continuous load path of 
sufficient strength and stiffness between the component 
and the supporting structure shall be provided. Local 
elements of the supporting structure shall be designed 
and constructed for the component forces where they 
control the design of the elements or their connec- 
tions. The component forces shall be those determined 
in Section 9.6.1.3, except that modifications to F p and 
R p due to anchorage conditions need not be considered. 
The design documents shall include sufficient informa- 
tion relating to the attachments to verify compliance with 
the requirements of this chapter. 

9.6.13 Seismic Forces. Seismic forces (F p ) shall be 
determined in accordance with Eq. 9.6.1.3-1: 



Fp = 



QAa p S DS W p 



M 



F p is not required to be taken as greater than 



(Eq. 9.6.13-1) 



F P = L6S DS I P W P 



and F p shall not be taken as less than 



F P = 0.3S DS I P W P 



(Eq. 9.6.13-2) 



(Eq. 9.6.13-3) 



where 



F p = seismic design force centered at the 

component's center of gravity and distributed 
relative to component's mass distribution 
S DS = spectral acceleration, short period, as 
determined from Section 9.4.1.2.5 

a p = component amplification factor that varies 
from 1.00 to 2.50 (select appropriate value 
from Table 9.6.2.2 or 9.6.3.2) 

l p ~ component importance factor that varies 

from 1.00 to 1.50 (see Section 9.6.1.5) 
W p = component operating weight 

R p = component response modification factor that 
varies from 1.50 to 5.00 (select appropriate 
value from Tables 9.6.2.2 or 9.6.3.2) 
z = height in structure of point of attachment of 
component with respect to the base. For 
items at or below the base, z shall be taken 
as 0. The value of z/h need not exceed 1.0 
h — average roof height of structure with respect 
to the base 

The force (F p ) shall be applied independently longi- 
tudinally, and laterally in combination with service loads 



Minimum Design Loads for Buildings and Other Structures 



159 



associated with the component. Combine horizontal and 
vertical load effects as indicated in Section 9.5.2.7 sub- 
stituting F p for the term Q E . The reliability /redundancy 
factor, p, is permitted to be taken equal to 1, 

When positive and negative wind loads exceed F p for 
nonbearing exterior wall, these wind loads shall govern 
the design. Similarly, when the building code horizontal 
loads exceed F p for interior partitions, these building 
code loads shall govern the design. 

In lieu of the forces determined in accordance with 
Eq. 9.6.1.3-1, accelerations at any level may be deter- 
mined by the modal analysis procedures of Section 9.5.6 
with /? == 1.0. Seismic forces shall be in accordance with 
Eq. 9.6.1.3-4: 



f p = -y^A* 



Rplh 



(Eq. 9.6.13-4) 



Where a, is the acceleration at level i obtained from 
the modal analysis and where A x is the torsional 
amplification factor determined by Eq, 9.5.5.5.2, Upper 
and lower limits of F p determined by Eq. 9.6.1.3-2 and 
-3 shall apply. 

9.6.1.4 Seismic Relative Displacements. Seismic rela- 
tive displacements (D p ) shall be determined in accor- 
dance with the following equations: 

For two connection points on the same Structure A 
or the same structural system, one at a height h x and the 
other at a height h y , D p shall be determined as 



Dp = &xA — &yA 



(Eq. 9.6.1.4-1) 



Alternatively, D p shall be permitted to be determined 
using modal procedures described in Section 9.5.6.8, 
using the difference in story deflections calculated for 
each mode and then combined using appropriate modal 
combination procedures. D p is not required to be taken 
as greater than 



$ xA — deflection at building Level x of Structure A, 

determined by an elastic analysis as defined 

in Section 9.5.5.7.1 
S yA = deflection at building Level y of Structure A, 

determined by an elastic analysis as defined 

in Section 9.5.5.7.1 
S yB — deflection at building Level y of Structure B, 

determined by an elastic analysis as defined 

in Section 9.5.5.7.1 
h x — height of Level x to which upper connection 

point is attached 
h y = height of Level y to which lower connection 

point is attached 
A aA = allowable story drift for Structure A as 

defined in Table 9.5.2.8 
A aB = allowable story drift for Structure B as 

defined in Table 9.5.2.8 
h sx = story height used in the definition of the 

allowable drift A a in Table 9.5.2.8, note that 

A a /h sx = the drift index 

The effects of seismic relative displacements shall be 
considered in combination with displacements caused by 
other loads as appropriate. 

9.6.1.5 Component Importance Factor. The compo- 
nent importance factor (I p ) shall be selected as follows: 

] p = 1.5 life safety component required to function 
after an earthquake (e.g., fire protection 
sprinkler system) 

l p = 1.5 component that contains hazardous content 

I p — 1.5 storage racks in structures open to the 
public (e.g., warehouse retails stores) 

I p = 1.0 all other components 

In addition, for structures in Seismic Use Group III: 

I p = 1.5 all components needed for continued 

operation of the facility or whose failure could 
impair the continued operation of the facility 



D p = (h x - hy)A aA /h sx (Eq. 9.6.1.4-2) 

For two connection points on separate Structures A or 
B or separate structural systems, one at a height h x and 
the other at a height h y , D p shall be determined as 

D p = \S xA \ + \S yB \ (Eq. 9.6.1.4-3) 

D p is not required to be taken as greater than 



D p = h x A aA /h sx + h v A aB /h sx 

(Eq. 9.6.1.4-4) 



where 



D p = relative seismic displacement that the 

component must be designed to accommodate 



9,6.1.6 Component Anchorage. Components shall be 
anchored in accordance with the following provisions. 

9.6.1.6.1 The force in the connected part shall be 
determined based on the prescribed forces for the 
component specified in Section 9.6.1.3. Where com- 
ponent anchorage is provided by shallow expansion 
anchors, shallow chemical anchors, or shallow (low 
deformability) cast-in-place anchors, a value of R p — 
1.5 shall be used in Section 9.6.1.3 to determine the 
forces in the connected part. 

9.6.1.6.2 Anchors embedded in concrete or masonry 
shall be proportioned to carry the least of the fol- 
lowing: 



160 



ASCE 7-02 



a. The design strength of the connected part, 

b. 1.3 times the force in the connected part due to 
the prescribed forces, or 

c. The maximum force that can be transferred 
to the connected part by the component struc- 
tural system. 

9.6.1.6.3 Determination of forces in anchors shall 
take into account the expected conditions of installa- 
tion including eccentricities and prying effects. 

9.6.1.6.4 Determination of force distribution of mul- 
tiple anchors at one location shall take into account 
the stiffness of the connected system and its ability 
to redistribute loads to other anchors in the group 
beyond yield. 

9.6.1.6.5 Powder driven fasteners shall not be used 
for tension load applications in Seismic Design Cate- 
gories D, E, and F unless approved for such loading. 

9.6.1.6.6 The design strength of anchors in concrete 
shall be determined in accordance with the provisions 
of Section 9.9. 

9.6.1.7 Construction Documents. Construction docu- 
ments shall be prepared to comply with the requirements 
of this Standard, as indicated in Table 9.6.1.7. 



9.6.2 Architectural Component Design. 

9.6.2.1 General. Architectural systems, components, or 
elements (hereinafter referred to as "components") listed 
in Table 9.6.2.2 and their attachments shall meet the 
requirements of Sections 9.6.2.2 through 9.6.2.9. 

9.6.2.2 Architectural Component Forces and Dis- 
placements. Architectural components shall meet the 
force requirements of Section 9.6.1.3 and Table 9.6.2.2. 

Components supported by chains or otherwise sus- 
pended from the structural system above are not required 
to meet the lateral seismic force requirements and seis- 
mic relative displacement requirements of this Section 
provided that they cannot be damaged to become a haz- 
ard or cannot damage any other component when subject 
to seismic motion and they have ductile or articulating 
connections to the structure at the point of attachment. 
The gravity design load for these items shall be three 
times their operating load. 

9.6.2.3 Architectural Component Deformation. Ar- 
chitectural components that could pose a life safety 
hazard shall be designed for the seismic relative dis- 
placement requirements of Section 9.6.1.4. Architectural 
components shall be designed for vertical deflection due 
to joint rotation of cantilever structural members. 



TABLE 9.6.1.7 
CONSTRUCTION DOCUMENTS 



Component Description 


Section Reference 


Required 

Seismic Design 

Categories 


Quality Assurance 


Design 


Exterior wall panels, including anchorage 


A.9.3.3.9 No. 1 


9.6.2.4 


D, E, F 


Suspended ceiling system, including anchorage 


A.9.3.3.9 No. 2 


9.6.2.6 


D, E, F 


Access floors, including anchorage 


A.9.3.3.9 No. 2 


9.6.2.7 


D, E, F 


Steel storage racks, including anchorage 


A.9.3.3.9 No. 2 


9.6.2.9 


D, E, F 


Glass in glazed curtain walls, glazed storefronts, and 
interior glazed partitions, including anchorage 


A.9.3.3.9 No. 3 


9.6.2.10 


D, E, F 


HVAC ductwork containing hazardous materials, 
including anchorage 


A.9.3.3.10No. 4 


9.6.3.10 


C, D, E 


Piping systems and mechanical units containing 
flammable, combustible, or highly toxic materials 


A.9.3.3.10No. 3 


9.6.3.11 
9.6.3.12 
9.6.3.13 


C, D, E, F 


Anchorage of electrical equipment for emergency or 
standby power systems 


A.9.3.3.10NO. 1 


9.6.3.14 


C, D, E, F 


Anchorage of all other electrical equipment 


A.9.3.3.10NO. 2 


9.6.3.14 


E, F 


Project-specific requirements for mechanical and 
electrical components and their anchorage 


A.9.3.4.5 


9.6.3 


C, D, E, F 



Minimum Design Loads for Buildings and Other Structures 



161 



TABLE 9.6.2.2 
ARCHITECTURAL COMPONENT COEFFICIENTS 



Architectural Component or Element 


a P 


R P * 


Interior Nonstructural Walls and Partitions 
Plain (unreinforced) masonry walls 
All other walls and partitions 


1 
1 


1.5 

2.5 


Cantilever Elements (Unbraced or Braced to Structural Frame Below Its Center of Mass) 
Parapets and cantilever interior nonstructural walls 
Chimneys and stacks when laterally braced or supported by the structural frame 


2,5 
2.5 


2.5 

2.5 


Cantilever Elements (Braced to Structural Frame Above Its Center of Mass) 
Parapets 

Chimneys and stacks 
Exterior nonstructural walls 


1.0 
1.0 
1.0 b 


2.5 
2.5 
2.5 


Exterior Nonstructural Wall Elements and Connections 
Wall element 

Body of wall panel connections 
Fasteners of the connecting system 


1 
1 

1.25 


2.5 
2.5 
1 


Veneer 
Limited deformability elements and attachments 
Low deformability elements and attachments 


1 
1 


2.5 
2.5 


Penthouses (Except when Framed by an Extension of the Building Frame) 
Ceilings 
All 


2.5 

i 


3.5 

2.5 


Cabinets 

Storage cabinets and laboratory equipment 


1 


2.5 


Access Floors 

Special access floors (designed in accordance with Section 9.6.2.7.2) 
All other 


1 
l 


2.5 
1.5 


Appendages and Ornamentations 


2.5 


2.5 


Signs and Billboards 


2.5 


2.5 


Other Rigid Components 

High deformability elements and attachments 
Limited deformability elements and attachments 
Low deformability materials and attachments 

Other Flexible Components 

High deformability elements and attachments 
Limited deformability elements and attachments 
Low deformability materials and attachments 


1 
1 
1 

2.5 

2.5 
2.5 


3.5 
2.5 
1.5 
3.5 

2.5 
1.5 



a A lower value for a p shall not be used unless justified by detailed dynamic analysis. The value for a p shall not be less than 1.00. 
The value of a p = 1 is for equipment generally regarded as rigid and rigidly attached. The value of a p =2.5 is for equipment 
generally regarded as flexible or flexibly attached. See Section 9.2.1 for definitions of rigid and flexible. 

b Where flexible diaphragms provide lateral support for walls and partitions, the design forces for anchorage to the diaphragm 
shall be as specified in Section 9.5.2.6. 



9.6.2.4 Exterior Nonstructural Wall Elements and 
Connections. 

9.6.2.4.1 General. Exterior nonstructural wall panels 
or elements that are attached to or enclose the 
structure shall be designed to resist the forces in 
accordance with Eq. 9.6.1.3-1 or 9.6.1.3-2, and shall 



accommodate movements of the structure resulting 
from response to the design basis ground motion, 
Dp, or temperature changes. Such elements shall be 
supported by means of positive and direct structural 
supports or by mechanical connections and fasteners. 
The support system shall be designed in accordance 
with the following: 



162 



ASCE 7-02 



a. Connections and panel joints shall allow for 
the story drift caused by relative seismic dis- 
placements (D p ) determined in Section 9.6.1.4, 
or 1/2 in. (13 mm), whichever is greatest. 

b. Connections to permit movement in the plane 
of the panel for story drift shall be sliding 
connections using slotted or oversize holes, 
connections that permit movement by bending 
of steel, or other connections that provide 
equivalent sliding or ductile capacity. 

c. The connecting member itself shall have suffi- 
cient ductility and rotation capacity to preclude 
fracture of the concrete or brittle failures at or 
near welds. 

d. All fasteners in the connecting system such 
as bolts, inserts, welds, and dowels and the 
body of the connectors shall be designed for 
the force (F p ) determined by Eq. 9.6.1.3-2 with 
values of R p and a p taken from Table 9.6.2.2 
applied at the center of mass of the panel. 

e. Anchorage using flat straps embedded in con- 
crete or masonry shall be attached to or hooked 
around reinforcing steel or otherwise terminated 
so as to effectively transfer forces to the rein- 
forcing steel or to assure that pullout of anchor- 
age is not the initial failure mechanism. 

9.6.2.4.2 Glass. Glass in glazed curtain walls and 
storefronts shall be designed and installed in accor- 
dance with Section 9.6.2,10. 

9.6.2.5 Out-of-Plane Bending. Transverse or out-of- 
plane bending or deformation of a component or 
system that is subjected to forces as determined in 
Section 9.6.2.2 shall not exceed the deflection capability 
of the component or system. 

9.6.2.6 Suspended Ceilings. Suspended ceilings shall 
be designed to meet the seismic force requirements 
of Section 9.6.2.6.1. In addition, suspended ceilings 
shall meet the requirements of either industry standard 
construction as modified in Section 9.6.2.6.2 or integral 
construction as specified in Section 9.6.2.6.3. 

9.6.2.6.1 Seismic Forces. Suspended ceilings shall 
be designed to meet the force requirements of 
Section 9.6.1.3. 

The weight of the ceiling, W pi shall include the 
ceiling grid and panels; light fixtures if attached to, 
clipped to, or laterally supported by the ceiling grid; 
and other components which are laterally supported 
by the ceiling. W p shall be taken as not less than 
4 lbs/ft 2 (19 N/m 2 ). 



The seismic force, F p , shall be transmitted through 
the ceiling attachments to the building structural 
elements or the ceiling-structure boundary. 

Design of anchorage and connections shall be in 
accordance with these provisions. 

9.6.2*6.2 Industry Standard Construction. Unless 
designed in accordance with Section 9.6.2.6.3, sus- 
pended ceilings shall be designed and constructed in 
accordance with this Section. 

9*6.2.6.2.1 Seismic Design Category C. Sus- 
pended ceilings in Seismic Design Category C 
shall be designed and installed in accordance with 
the CISC A recommendations for seismic Zones 0- 
2, (Ref. 9.6-16), except that seismic forces shall 
be determined in accordance with Sections 9.6.1.3 
and 9.6.2.6.1. 

Sprinkler heads and other penetrations in Seis- 
mic Design Category C shall have a minimum of 
1/4 in, (6 mm) clearance on all sides. 

9.6.2.6.2.2 Seismic Design Categories D, E, and 
F. Suspended ceilings in Seismic Design Cate- 
gories D, E, and F shall be designed and installed 
in accordance with the CISCA recommendations 
for seismic Zones 3-4 (Ref. 9.6-17) and the addi- 
tional requirements listed in this subsection. 

a. A heavy duty 7" -bar grid system shall 
be used. 

b. The width of the perimeter supporting 
closure angle shall be not less than 2.0 in. 
(50 mm). In each orthogonal horizontal 
direction, one end of the ceiling grid shall 
be attached to the closure angle. The other 
end in each horizontal direction shall have 
a 3/4 in. (19 mm) clearance from the wall 
and shall rest upon and be free to slide on a 
closure angle. 

c. For ceiling areas exceeding 1000 ft 2 
(92.9 m 2 ), horizontal restraint of the ceil- 
ing to the structural system shall be pro- 
vided. The tributary areas of the horizontal 
restraints shall be approximately equal. 

Exception: Rigid braces are permitted to 
be used instead of diagonal splay wires. 
Braces and attachments to the structural 
system above shall be adequate to limit 
relative lateral deflections at point of 
attachment of ceiling grid to less than 
1/4 in. (6 mm) for the loads prescribed in 
Section 9.6.1.3. 



Minimum Design Loads for Buildings and Other Structures 



163 



d. For ceiling areas exceeding 2500 ft 2 
(232 m 2 ) ? a seismic separation joint or 
full height partition that breaks the ceil- 
ing up into areas not exceeding 2500 ft 2 
shall be provided unless structural analyses 
are performed of the ceiling bracing sys- 
tem for the prescribed seismic forces which 
demonstrate ceiling system penetrations and 
closure angles provide sufficient clearance 
to accommodate the additional movement. 
Each area shall be provided with closure 
angles in accordance with Item b and hor- 
izontal restraints or bracing in accordance 
with Item c. 

e. Except where rigid braces are used to limit 
lateral deflections, sprinkler heads and other 
penetrations shall have a 2 in. (50 mm) over- 
size ring, sleeve, or adapter through the ceil- 
ing tile to allow for free movement of at least 
1 in. (25 mm) in all horizontal directions. 
Alternatively, a swing joint that can accom- 
modate 1 in. (25 mm) of ceiling movement 
in all horizontal directions are permitted 
to be provided at the top of the sprinkler 
head extension. 

f. Changes in ceiling plan elevation shall be 
provided with positive bracing. 

g. Cable trays and electrical conduits shall be 
supported independently of the ceiling. 

h. Suspended ceilings shall be subject to the 
special inspection requirements of Section A. 
9.3.3,9 of this Standard. 

9.6.2.6.3 Integral Ceiling/Sprinkler Construction. 
As an alternative to providing large clearances around 
sprinkler system penetrations through ceiling systems, 
the sprinkler system and ceiling grid are permitted to 
be designed and tied together as an integral unit. Such 
a design shall consider the mass and flexibility of all 
elements involved, including: ceiling system, sprin- 
kler system, light fixtures, and mechanical (HVAC) 
appurtenances. The design shall be performed by a 
registered design professional. 

9,6.2.7 Access Floors. 

9.6.2.7.1 General. Access floors shall be designed to 
meet the force provisions of Section 9.6.1.3 and the 
additional provisions of this Section. The weight of 
the access floor, W p , shall include the weight of the 
floor system, 100% of the weight of all equipment 
fastened to the floor, and 25% of the weight of 
all equipment supported by, but not fastened to the 
floor. The seismic force, F pi shall be transmitted 



from the top surface of the access floor to the 
supporting structure. 

Overturning effects of equipment fastened to the 
access floor panels also shall be considered. The 
ability of "slip on" heads for pedestals shall be 
evaluated for suitability to transfer overturning effects 
of equipment. 

When checking individual pedestals for overturn- 
ing effects, the maximum concurrent axial load shall 
not exceed the portion of W p assigned to the pedestal 
under consideration. 

9.6.2.7.2 Special Access Floors. Access floors shall 
be considered to be "special access floors" if they are 
designed to comply with the following considerations: 

1. Connections transmitting seismic loads con- 
sist of mechanical fasteners, concrete anchors, 
welding, or bearing. Design load capacities 
comply with recognized design codes and/or 
certified test results. 

2. Seismic loads are not transmitted by fric- 
tion, produced solely by the effects of grav- 
ity, powder-actuated fasteners (shot pins), 
or adhesives. 

3. The design analysis of the bracing system 
includes the destabilizing effects of individual 
members buckling in compression. 

4. Bracing and pedestals are of structural or 
mechanical shape produced to ASTM specifi- 
cations that specify minimum mechanical prop- 
erties. Electrical tubing shall not be used. 

5. Floor stringers that are designed to carry axial 
seismic loads and that are mechanically fas- 
tened to the supporting pedestals are used. 

9.6.2.8 Partitions. 

9.6.2.8.1 General. Partitions that are tied to the 
ceiling and all partitions greater than 6 ft (1.8 m) 
in height shall be laterally braced to the building 
structure. Such bracing shall be independent of any 
ceiling splay bracing. Bracing shall be spaced to 
limit horizontal deflection at the partition head to 
be compatible with ceiling deflection requirements as 
determined in Section 9.6.2.6 for suspended ceilings 
and Section 9.6.2.2 for other systems. 

9.6.2.8.2 Glass. Glass in glazed partitions shall 
be designed and installed in accordance with 
Section 9.6.2.10. 

9.6.2.9 Steel Storage Racks. Steel storage racks sup- 
ported at the base of the structure shall be designed 



164 



ASCE 7-02 



to meet the force requirements of Section 9.14. Steel 
storage racks supported above the base of the struc- 
ture shall be designed to meet the force requirements 
of Sections 9.6.1 and 9.6.2. 

9.6.2.10 Glass In Glazed Curtain Walls, Glazed 
Storefronts, and Glazed Partitions. 

9.6.2.10.1 General. Glass in glazed curtain walls, 
glazed storefronts, and glazed partitions shall meet the 
relative displacement requirement of Eq. 9.6.2.10.1-1: 



^fallout > L25D p I 



(Eq. 9.6.2.10.1-1) 



or 0.5 in. (13 mm), whichever is greater where 

Afajjout = the relative seismic displacement (drift) 
causing glass fallout from the curtain 
wall, storefront wall, or partition 
(Section 9.6.2.10.2) 
D p — the relative seismic displacement that the 
component must be designed to 
accommodate (Eq. 9.6.1.4-1). D p shall be 
applied over the height of the glass 
component under consideration 
/ = the occupancy importance factor 
(Table 9.1.4) 



3. Annealed or heat-strengthened laminated 
glass in single thickness with interlayer no 
less than 0.030 in. (0.76 mm) that is cap- 
tured mechanically in a wall system glaz- 
ing pocket, and whose perimeter is secured 
to the frame by a wet glazed gunable 
curing elastomeric sealant perimeter bead 
of 1/2 in. (13 mm) minimum glass contact 
width, or other approved anchorage system 
shall be exempted from the provisions of 
Eq. 9.6.2.10.1-1. 

9.6.2.10.2 Seismic Drift Limits for Glass Compo- 
nents. A f a ii out t the drift causing glass fallout from 
the curtain wall, storefront, or partition shall be 
determined in accordance with Ref. 9.6-21, or by 
engineering analysis. 

9.6.3 Mechanical and Electrical Component Design. 



9.6.3.1 General. Attachments and equipment supports 
for the mechanical and electrical systems, compo- 
nents, or elements (hereinafter referred to as "compo- 
nents") shall meet the requirements of Sections 9.6.3.2 
through 9.6.3.16. 



Exceptions: 

1. Glass with sufficient clearances from its 
frame such that physical contact between the 
glass and frame will not occur at the design 
drift, as demonstrated by Eq. 9.6.2.10.1-2, 
shall be exempted from the provisions of 
Eq. 9.6.2.10.1-1: 



D cle ar > 1.25 D p 



(Eq. 9.6.2.10.1-2) 



where 

U clear ~ 

h r 



ley 1 + 



h p c 2 
bpCi 



v p — the height of the rectangular glass 
b p = the width of the rectangular glass 
c\ = the clearance (gap) between the 
vertical glass edges and the frame, 
and 
c 2 = the clearance (gap) between the 
horizontal glass edges and the 
frame 
2. Fully tempered monolithic glass in Seis- 
mic Use Groups I and II located no more 
than 10 ft (3 m) above a walking surface 
shall be exempted from the provisions of 
Eq. 9.6.2.10.1-1. 



9.6.3.2 Mechanical and Electrical Component Forces 
and Displacements. Mechanical and electrical compo- 
nents shall meet the force and seismic relative dis- 
placement requirements of Sections 9.6.1.3, 9.6.1.4, and 
Table 9.6.3.2. 

Components supported by chains or otherwise sus- 
pended from the structural system above are not required 
to meet the lateral seismic force requirements and seis- 
mic relative displacement requirements of this Section 
provided they are designed to prevent damage to them- 
selves or causing damage to any other component when 
subject to seismic motion. Such supports shall have duc- 
tile or articulating connections to the structure at the 
point of attachment. The gravity design load for these 
items shall be three times their operating load. 

9.6.3.3 Mechanical and Electrical Component 
Period. The fundamental period of the mechanical and 
electrical component (and its attachment to the build- 
ing), T p , shall be determined by the following equation 
provided that the component and attachment can be rea- 
sonably represented analytically by a simple spring and 
mass single degree of freedom system: 



T» = 2tt 



/ w p 

K P g 



(Eq. 9.6.3.3) 



Minimum Design Loads for Buildings and Other Structures 



165 



TABLE 9.6.3.2 

MECHANICAL AND ELECTRICAL COMPONENTS SEISMIC 

COEFFICIENTS 



Mechanical and Electrical 
Component or Element b 




R P 


General Mechanical Equipment 
Boilers and furnaces 
Pressure vessels on skirts and free-standing 

stacks 
Cantilevered chimneys 
Other 


1.0 

2.5 
2.5 
2.5 
1.0 


2.5 
2.5 
2.5 
2.5 
2.5 


Manufacturing and Process Machinery 
General 
Conveyors (non-personnel) 


1.0 

2.5 


2.5 
2.5 


Piping Systems 

High deformability elements and attachments 
Limited deformability elements and attachments 
Low deformability elements and attachments 


1.0 
1.0 
1.0 


3.5 
2.5 
1.5 


HVAC Systems 
Vibration isolated 
Nonvibration isolated 
Mounted in-line with ductwork 
Other 


2.5 
1.0 
1.0 
1.0 


2.5 
2.5 
2.5 
2.5 


Elevator Components 


1.0 


2.5 


Escalator Components 


1.0 


2.5 


Trussed Towers (free-standing or guyed) 


2.5 


2.5 


General Electrical 

Distribution systems (bus ducts, conduit, cable tray) 
Equipment 


2.5 
1.0 


5.0 

2.5 


Lighting Fixtures 


1.0 


1.5 



a A lower value for a p shall not be used unless justified by detailed dynamic analyses. The 
value for a p shall not be less than 1.00. The value of a p = 1 is for equipment generally 
regarded as rigid or rigidly attached. The value of a p = 2.5 is for equipment generally 
regarded as flexible or flexibly attached. See Section 9.2.2 for definitions of rigid and flexible. 
b Components mounted on vibration isolation systems shall have a bumper restraint or 
snubber in each horizontal direction. The design force shall be taken as 2F p if the maximum 
clearance (air gap) between the equipment support frame and restraint is greater than 1/4 in. 
If the maximum clearance is specified on the construction documents to be not greater than 
1/4 in., the design force may be taken as F p . 



where 

T p — component fundamental period 

W p = component operating weight 
g = gravitational acceleration 

K p — stiffness of resilient support system of the 
component and attachment, determined in 
terms of load per unit deflection at the center 
of gravity of the component 

Note that consistent units must be used. 



Otherwise, determine the fundamental period of the 
component in seconds (T p ) from experimental test data 
or by a properly substantiated analysis. 



9.6.3,4 Mechanical and Electrical Component Att- 
achments. The stiffness of mechanical and electrical 
component attachments shall be designed such that 
the load path for the component performs its 
intended function. 



166 



ASCE 7-02 



9.6.3.5 Component Supports. Mechanical and electri- 
cal component supports and the means by which they 
are attached to the component shall be designed for the 
forces determined in Section 9.6.1.3 and in conformance 
with Sections 9.8 through 9.12, as appropriate, for the 
materials comprising the means of attachment. Such sup- 
ports include structural members, braces, frames, skirts, 
legs, saddles, pedestals, cables, guys, stays, snubbers, 
and tethers, as well as element forged or cast as a part 
of the mechanical or electrical component. If standard or 
proprietary supports are used, they shall be designed by 
either load rating (i.e., testing) or for the calculated seis- 
mic forces. In addition, the stiffness of the support, when 
appropriate, shall be designed such that the seismic load 
path for the component performs its intended function. 

Component supports shall be designed to accommo- 
date the seismic relative displacements between points of 
support determined in accordance with Section 9.6.1.4. 

In addition, the means by which supports are attached 
to the component, except when integral (i.e., cast or 
forged), shall be designed to accommodate both the 
forces and displacements determined in accordance with 
Sections 9.6.1.3 and 9.6.1.4. If the value of I p = 1.5 
for the component, the local region of the support 
attachment point to the component shall be evaluated for 
the effect of the load transfer on the component wall. 

9.6.3.6 Component Certification. Architectural, mech- 
anical, and electrical components shall comply with the 
force requirements of Section 9.6. Components desig- 
nated with an I p greater than 1.0 in Seismic Design 
Category C, D, E, and F shall meet additional require- 
ments of Section A. 9. 3. 4. 5 and in particular, mechanical 
and electrical equipment which must remain operable 
following the design earthquake shall demonstrate oper- 
ability by shake table testing or experience data. 

The manufacturer's certificate of compliance indicat- 
ing compliance with this Section shall be submitted to 
the authority having jurisdiction when required by the 
contract documents or when required by the regula- 
tory agency. 

9.6.3.7 Utility and Service Lines at Structure Inter- 
faces. At the interface of adjacent structures or portions 
of the same structure that may move independently, 
utility lines shall be provided with adequate flexibility 
to accommodate the anticipated differential movement 
between the portions that move independently. Differ- 
ential displacement calculations shall be determined in 
accordance with Section 9.6.1.4. 

9.6.3.8 Site-Specific Considerations. The possible in- 
terruption of utility service shall be considered in relation 
to designated seismic systems in Seismic Use Group III 
as defined in Section 9.1.3.4. Specific attention shall be 



given to the vulnerability of underground utilities and 
utility interfaces between the structure and the ground 
where Site Class E or F soil is present, and where the 
seismic coefficient S^s at the underground utility or at 
the base of the structure is equal to or greater than 0.33. 

9.6.3.9 Storage Tanks Mounted in Structures. Sto- 
rage tanks, including their attachments and supports, 
shall be designed to meet the force requirements of 
Section 9.14. 

9.6.3.10 HVAC Ductwork. Attachments and supports 
for HVAC ductwork systems shall be designed to meet 
the force and displacement provisions of Sections 9.6. 1 .3 
and 9.6.1.4 and the additional provisions of this Section. 
In addition to their attachments and supports, ductwork 
systems designated as having an I p — 1.5 themselves 
shall be designed to meet the force and displacement 
provisions of Sections 9.6.1.3 and 9.6.1.4 and the addi- 
tional provisions of this Section. Where HVAC ductwork 
runs between structures that could displace relative to 
one another and for seismically isolated structures where 
the HVAC ductwork crosses the seismic isolation inter- 
face, the HVAC ductwork shall be designed to accom- 
modate the seismic relative displacements specified in 
Section 9.6.1.4. 

Seismic restraints are not required for HVAC ducts 
with I p = 1.0 if either of the following conditions 
are met: 

a. HVAC ducts are suspended from hangers 12 in. 
(305 mm) or less in length from the top of the duct 
to the supporting structure. The hangers shall be 
detailed to avoid significant bending of the hangers 
and their attachments, 



or 



b. HVAC ducts have a cross-sectional area of less 
than 6 ft 2 (0.557 m 2 ). 

HVAC duct systems fabricated and installed in accor- 
dance with standards approved by the authority having 
jurisdiction shall be deemed to meet the lateral bracing 
requirements of this Section. 

Equipment items installed in-line with the duct system 
(e.g., fans, heat exchangers, and humidifiers) weighing 
more than 75 lb (344 N) shall be supported and later- 
ally braced independent of the duct system and shall 
meet the force requirements of Section 9.6.1.3. Appur- 
tenances such as dampers, louvers, and diffusers shall be 
positively attached with mechanical fasteners. Unbraced 
piping attached to in-line equipment shall be provided 
with adequate flexibility to accommodate differential dis- 
placements. 



Minimum Design Loads for BusSdengs and Other Structures 



167 



9.6.3.11 Piping Systems. Attachments and supports for 
piping systems shall be designed to meet the force 
and displacement provisions of Sections 9.6.1.3 and 
9.6.1.4 and the additional provisions of this Section. In 
addition to their attachments and supports, piping sys- 
tems designated as having I p — 1.5 themselves shall be 
designed to meet the force and displacement provisions 
of Sections 9.6.1.3 and 9.6.1.4 and the additional provi- 
sions of this Section. Where piping systems are attached 
to structures that could displace relative to one another 
and for seismicaily isolated structures where the piping 
system crosses the seismic isolation interface, the piping 
system shall be designed to accommodate the seismic 
relative displacements specified in Section 9.6.1.4. 

Seismic effects that shall be considered in the design 
of a piping system include the dynamic effects of the 
piping system, its contents, and, when appropriate, its 
supports. The interaction between the piping system and 
the supporting structures, including other mechanical and 
electrical equipment shall also be considered. 



ceramics), 25% of the piping material 
minimum specified tensile strength. 

4. For threaded connections in piping con- 
structed with non-ductile materials, 20% of 
the piping material minimum specified ten- 
sile strength. 

b. Provisions shall be made to mitigate seismic 
impact for piping components constructed of 
nonductile materials or in cases where mate- 
rial ductility is reduced (e.g., low temperature 
applications). 

c. Piping shall be investigated to ensure that the 
piping has adequate flexibility between sup- 
port attachment points to the structure, ground, 
other mechanical and electrical equipment, or 
other piping. 

d. Piping shall be investigated to ensure that the 
interaction effects between it and other piping 
or constructions are acceptable. 



9.6.3.11.1 Pressure Piping Systems. Pressure piping 
systems designed and constructed in accordance with 
ASME B31, Code for Pressure Piping (Ref. 9.6-3) 
shall be deemed to meet the force, displacement, and 
other provisions of this Section. In lieu of specific 
force and displacement provisions provided in the 
ASME B31, the force and displacement provisions 
of Sections 9.6.1.3 and 9.6.1.4 shall be used. 

9.6.3.11.2 Fire Protection Sprinkler Systems. Fire 
protection sprinkler systems designed and constructed 
in accordance with NFPA 13, Standard for the Instal- 
lation of Sprinkler Systems (Ref. 9.6-12) shall be 
deemed to meet the other requirements of this Section, 
except the force and displacement requirements of 
Sections 9.6.1.3 and 9.6.1.4 shall be satisfied. 

9.6.3.11.3 Other Piping Systems. Piping designated 
as having an I p = 1.5 but not designed and con- 
structed in accordance with ASME B31 (Ref. 9.6-3) 
or NFPA 13 (Ref. 9.6-12) shall meet the following: 

a. The design strength for seismic loads in com- 
bination with other service loads and appro- 
priate environmental effects shall not exceed 
the following: 

1. For piping systems constructed with ductile 
materials (e.g., steel, aluminum, or copper), 
90% of the piping material yield strength. 

2. For threaded connections with ductile 
materials, 70% of the piping material yield 
strength. 

3. For piping constructed with nonductile 
materials (e.g., plastic, cast iron, or 



9.6.3.11.4 Supports and Attachments for Other 
Piping. Attachments and supports for piping not 
designed and constructed in accordance with ASME 
B31 [Ref. 9.6-3] or NFPA 13 [Ref. 9.6-12] shall meet 
the following provisions: 

a. Attachments and supports transferring seismic 
loads shall be constructed of materials suitable 
for the application and designed and constructed 
in accordance with a nationally recognized 
structural code such as, when constructed of 
steel, the AISC Manual of Steel Construction 
(Ref. 9.8-1 or 9.8-2) or MSS SP-58, Pipe Hang- 
ers and Supports -Materials, Design, and Man- 
ufacture (Ref. 9.6-15). 

b. Attachments embedded in concrete shall be 
suitable for cyclic loads. 

c. Rod hangers shall not be used as seismic sup- 
ports unless the length of the hanger from the 
supporting structure is 12 in. (305 mm) or less. 
Rod hangers shall not be constructed in a man- 
ner that subjects the rod to bending moments. 

d. Seismic supports are not required for: 

1. Ductile piping in Seismic Design Cate- 
gory D, E, or F designated as having an 
I p = 1.5 and a nominal pipe size of 1 in. 
(25 mm) or less when provisions are made 
to protect the piping from impact or to avoid 
the impact of larger piping or other mechan- 
ical equipment. 

2. Ductile piping in Seismic Design Cate- 
gory C designated as having an I p = 1.5 
and a nominal pipe size of 2 in. (50 mm) 



168 



ASCE 7-02 



or less when provisions are made to pro- 
tect the piping from impact or to avoid the 
impact of larger piping or other mechani- 
cal equipment. 

3. Ductile piping in Seismic Design Cate- 
gory D, E, or F designated as having an 
I p — 1.0 and a nominal pipe size of 3 in. 
(75 mm) or less. 

4. Ductile piping in Seismic Design Cate- 
gory A, B, or C designated as having an 
I p — 1 .0 and a nominal pipe size of 6 in. 
(150 mm) or less. 

e. Seismic supports shall be constructed so that 
support engagement is maintained. 

9.6.3.12 Boilers and Pressure Vessels. Attachments 
and supports for boilers and pressure vessels shall be 
designed to meet the force and displacement provisions 
of Sections 9.6.1.3 and 9.6.1,4 and the additional pro- 
visions of this Section. In addition to their attachments 
and supports, boilers and pressure vessels designated as 
having an I p = 1.5 themselves shall be designed to meet 
the force and displacement provisions of Sections 9.6.1.3 
and 9.6.1.4. 

The seismic design of a boiler or pressure vessel shall 
include analysis of the following: the dynamic effects 
of the boiler or pressure vessel, its contents, and its 
supports; sloshing of liquid contents; loads from attached 
components such as piping; and the interaction between 
the boiler or pressure vessel and its support. 

9.6.3.12.1 ASME Boilers and Pressure Vessels. 
Boilers or pressure vessels designed in accordance 
with the ASME Boiler and Pressure Vessel Code 
(Ref. 9.6-4) shall be deemed to meet the force, dis- 
placement, and other requirements of this Section. In 
lieu of the specific force and displacement provisions 
provided in the ASME code, the force and displace- 
ment provisions of Sections 9.6.1.3 and 9.6.1.4 shall 
be used. 

9.6.3.12.2 Other Boilers and Pressure Vessels. 
Boilers and pressure vessels designated as having an 
I p = 1.5 but not constructed in accordance with the 
provisions of the ASME code (Ref. 9.6-4) shall meet 
the following provisions: 

a. The design strength for seismic loads in com- 
bination with other service loads and appro- 
priate environmental effects shall not exceed 
the following: 

1. For boilers and pressure vessels constructed 
with ductile materials (e.g., steel, aluminum, 
or copper), 90% of the material minimum 
specified yield strength. 



2. For threaded connections in boilers or pres- 
sure vessels or their supports constructed 
with ductile materials, 70% of the material 
minimum specified yield strength. 

3. For boilers and pressure vessels constructed 
with nonductile materials (e.g., plastic, cast 
iron, or ceramics), 25% of the material 
minimum specified tensile strength. 

4. For threaded connections in boilers or pres- 
sure vessels or their supports constructed 
with nonductile materials, 20% of the mate- 
rial minimum specified tensile strength. 

b. Provisions shall be made to mitigate seismic 
impact for boiler and pressure vessel compo- 
nents constructed of nonductile materials or in 
cases where material ductility is reduced (e.g., 
low temperature applications). 

c. Boilers and pressure vessels shall be inves- 
tigated to ensure that the interaction effects 
between them and other constructions are 
acceptable. 

9.6.3.12.3 Supports and Attachments for Other 
Boilers and Pressure Vessels. Attachments and sup- 
ports for boilers and pressure vessels shall meet the 
following provisions: 

a. Attachments and supports transferring seismic 
loads shall be constructed of materials suit- 
able for the application and designed and 
constructed in accordance with nationally rec- 
ognized structural code such as, when con- 
structed of steel, the AISC Manual of Steel 
Construction (Ref. 9.8-1 or 9.8-2). 

b. Attachments embedded in concrete shall be 
suitable for cyclic loads. 

c. Seismic supports shall be constructed so that 
support engagement is maintained. 

9.6.3.13 Mechanical Equipment, Attachments, and 
Supports. Attachments and supports for mechanical 
equipment not covered in Sections 9.6.3.8 through 
9.6.3.12 or 9.6.3.16 shall be designed to meet the force 
and displacement provisions of Sections 9.6.1.3 and 
9.6.1.4 and the additional provisions of this Section. In 
addition to their attachments and supports, such mechan- 
ical equipment designated as having an I p = 1.5, itself, 
shall be designated to meet the force and displacement 
provisions of Sections 9.6.1.3 and 9.6.1.4 and the addi- 
tional provisions of this Section. 

The seismic design of mechanical equipment, attach- 
ments, and their supports shall include analysis of the 
following: the dynamic effects of the equipment, its con- 
tents, and, when appropriate, its supports. The interaction 



Minimum Design Loads for Buildings and Other Structures 



169 



between the equipment and the supporting structures, 
including other mechanical and electrical equipment, 
shall also be considered. 

9.6.3.13.1 Mechanical Equipment. Mechanical eq- 
uipment designated as having an I p = 1.5 shall meet 
the following provisions. 

a. The design strength for seismic loads in com- 
bination with other service loads and appro- 
priate environmental effects shall not exceed 
the following: 

1. For mechanical equipment constructed with 
ductile materials (e.g., steel, aluminum, or 
copper), 90% of the equipment material 
minimum specified yield strength. 

2. For threaded connections in equipment con- 
structed with ductile materials, 70% of the 
material minimum specified yield strength. 

3. For mechanical equipment constructed with 
nonductile materials (e.g., plastic, cast iron, 
or ceramics), 25% of the equipment material 
minimum tensile strength. 

4. For threaded connections in equipment con- 
structed with nonductile materials, 20% 
of the material minimum specified yield 
strength. 

b. Provisions shall be made to mitigate seismic 
impact for equipment components constructed 
of nonductile materials or in cases where mate- 
rial ductility is reduced (e.g., low temperature 
applications). 

c. The possibility for loadings imposed on the 
equipment by attached utility or service lines 
due to differential motions of points of support 
from separate structures shall be evaluated. 

9.6.3.13.2 Attachments and Supports for Mechan- 
ical Equipment. Attachments and supports for 
mechanical equipment shall meet the following pro- 
visions: 

a. Attachments and supports transferring seismic 
loads shall be constructed of materials suitable 
for the application and designed and constructed 
in accordance with a nationally recognized 
structural code such as, when constructed of 
steel, AISC, Manual of Steel Construction 
(Ref. 9.8-1 or 9.8-2). 

b. Friction clips shall not be used for anchor- 
age attachment. 

c. Expansion anchors shall not be used for mecha- 
nical equipment rated over 10 hp (7.45 kW). 



Exception: Undercut expansion anchors. 

d. Drilled and grouted-in-place anchors for tensile 
load applications shall use either expansive 
cement or expansive epoxy grout. 

e. Supports shall be specifically evaluated if weak- 
axis bending of light-gauge support steel is 
relied on for the seismic load path. 

f. Components mounted on vibration isolation 
systems shall have a bumper restraint or snub- 
ber in each horizontal direction. The design 
force shall be taken as 2F P . The intent is to pre- 
vent excessive movement and to avoid fracture 
of support springs and any nonductile compo- 
nents of the isolators. 

g. Seismic supports shall be constructed so that 
support engagement is maintained. 

9.6.3.14 Electrical Equipment, Attachments, and 
Supports. Attachments and supports for electrical 
equipment shall be designed to meet the force and 
displacement provisions of Sections 9.6.1.3 and 9.6.1.4 
and the additional provisions of this Section. In 
addition to their attachments and supports, electrical 
equipment designated as having I p = 1.5, itself, shall be 
designed to meet the force and displacement provisions 
of Sections 9.6.1.3 and 9.6.1.4 and the additional 
provisions of this Section. 

The seismic design of other electrical equipment shall 
include analysis of the following: the dynamic effects 
of the equipment, its contents, and when appropriate, 
its supports. The interaction between the equipment and 
the supporting structures, including other mechanical and 
electrical equipment, shall also be considered. Where 
conduit, cable trays, or similar electrical distribution 
components are attached to structures that could displace 
relative to one another and for seismically isolated 
structures where the conduit or cable trays cross the 
seismic isolation interface, the conduit or cable trays 
shall be designed to accommodate the seismic relative 
displacement specified in Section 9.6.1.4. 

9.63.14.1 Electrical Equipment. Electrical equip- 
ment designated as having an I p = 1.5 shall meet the 
following provisions: 

a. The design strength for seismic loads in com- 
bination with other service loads and appro- 
priate environmental effects shall not exceed 
the following: 

1. For electrical equipment constructed with 
ductile material (e.g., steel, aluminum, or 
copper), 90% of the equipment material 
minimum specified yield strength. 



170 



ASCE 7-02 



2. For threaded connections in equipment con- 
structed with ductile materials, 70% of the 
material minimum specified yield strength. 

3. For electrical equipment constructed with 
nonductile materials (e.g., plastic, cast iron, 
or ceramics), 25% of the equipment material 
minimum tensile strength. 

4. For threaded connections in equipment con- 
structed with nonductile materials, 20% 
of the material minimum specified yield 
strength. 

b. Provisions shall be made to mitigate seismic 
impact for equipment components constructed 
of nonductile materials or in cases where mate- 
rial ductility is reduced (e.g., low-temperature 
applications). 

c. The possibility for loadings imposed on the 
equipment by attached utility or service lines 
due to differential motion of points of support 
from separate structures shall be evaluated. 

d. Batteries on racks shall have wraparound 
restraints to ensure that the batteries will not 
fall off the rack. Spacers shall be used between 
restraints and cells to prevent damage to cases. 
Racks shall be evaluated for sufficient lateral 
and longitudinal load capacity. 

e. Internal coils of dry type transformers shall be 
positively attached to their supporting substruc- 
ture within the transformer enclosure. 

f. Slide out components in electrical control pan- 
els shall have a latching mechanism to hold 
contents in place. 

g. Structural design of electrical cabinets shall be 
in conformance with standards of the industry 
that are acceptable to the authority having juris- 
diction. Large cutouts in the lower shear panel 
shall be specifically evaluated if an evaluation 
is not provided by the manufacturer. 

h. The attachment of additional items weighing 
more than 100 lb (440 N) shall be specifically 
evaluated if not provided by the manufacturer. 

9.6.3.14.2 Attachments and Supports for Electri- 
cal Equipment. Attachments and supports for elec- 
trical equipment shall meet the following provisions: 

a. Attachments and supports transferring seismic 
loads shall be constructed of materials suitable 
for the application and designed and constructed 
in accordance with a nationally recognized 
structural code such as, when constructed of 
steel, AISC, Manual of Steel Construction 
(Ref. 9.8-1 or 9.8-2). 



b. Friction clips shall not be used for anchor- 
age attachment. 

c. Oversized washers shall be used at bolted 
connections through the base sheet metal if the 
base is not reinforced with stiff eners. 

d. Supports shall be specifically evaluated if weak- 
axis bending of light-gauge support steel is 
relied on for the seismic load path. 

e. The supports for linear electrical equipment 
such as cable trays, conduit, and bus ducts shall 
be designed to meet the force and displacement 
provisions of Sections 9.6.1.3 and 9.6.1.4 only 
if any of the following situations apply: 

Supports are cantilevered up from the floor, 

Supports include bracing to limit deflection, 

Supports are constructed as rigid welded frames, 

Attachments into concrete utilize nonexpanding 
insets, shot pins, or cast iron embedments, or 

Attachments utilize spot welds, plug welds, 
or minimum size welds as defined by AISC 
(Ref. 9.8-1 or 9.8-2) 

f. Components mounted on vibration isolation 
systems shall have a bumper restraint or snub- 
ber in each horizontal direction, and verti- 
cal restraints shall be provided where required 
to resist overturning. Isolator housings and 
restraints shall not be constructed of cast 
iron or other materials with limited ductility. 
(See additional design force requirements in 
Table 9.6.3.2.) A viscoelastic pad or similar 
material of appropriate thickness shall be used 
between the bumper and equipment item to 
limit the impact load. 

9.6.3.15 Alternative Seismic Qualification Methods. 
As an alternative to the analysis methods implicit in the 
design methodology described above, equipment testing 
is an acceptable method to determine seismic capacity. 
Thus, adaptation of a nationally recognized standard for 
qualification by testing that is acceptable to the authority 
having jurisdiction is an acceptable alternative, so long 
as the equipment seismic capacity equals or exceeds the 
demand expressed in Sections 9.6.1.3 and 9.6.1.4. 

9.6.3.16 Elevator Design Requirements. 

9,6.3.16.1 Reference Document. Elevators shall 
meet the force and displacement provisions of 
Section 9.6.3.2 unless exempted by either Section 
9.1.2:1 or Section 9.6.1. Elevators designed in accor- 
dance with the seismic provisions of the ASME Safety 
Code for Elevators and Escalators (Ref. 9.6-1) shall 
be deemed to meet the seismic force requirements of 
this Section, except as modified below. 



Minimum Design Loads for Buildings and Other Structures 



171 



9.6.3.16.2 Elevators and Hoistway Structural Sys- 
tem. Elevators and hoistway structural systems shall 
be designed to meet the force and displacement 
provisions of Sections 9.6.1.3 and 9.6.1.4. 

9.6.3.16.3 Elevator Machinery and Controller 
Supports and Attachments. Elevator machinery and 
controller supports and attachments shall be designed 
to meet with the force and displacement provisions of 
Sections 9.6.1.3 and 9.6.1.4. 

9.6.3.16.4 Seismic Controls. Seismic switches shall 
be provided for all elevators addressed by Section 
9.6.3.1.6.1 including those meeting the requirements 
of the ASME reference, provided they operate with a 
speed of 150 ft/min (46 m/min) or greater. 

Seismic switches shall provide an electrical signal 
indicating that structural motions are of such a 
magnitude that the operation of elevators may be 
impaired. Upon activation of the seismic switch, 
elevator operations shall conform to provisions in 
the ASME Safety Code for Elevators and Escalators 
(Ref. 9.6-1) except as noted below. The seismic 
switch shall be located at or above the highest floor 
serviced by the elevators. The seismic switch shall 
have two horizontal perpendicular axes of sensitivity. 
Its trigger level shall be set to 30% of the acceleration 
of gravity. 

In facilities where the loss of the use of an elevator 
is a life safety issue, the elevator shall only be used 
after the seismic switch has triggered provided that: 

1. The elevator shall operate no faster than the 
service speed, 

2. Before the elevator is occupied, it is operated 
from top to bottom and back to top to verify 
that it is operable, and 

3. The individual putting the elevator back in 
service shall ride the elevator from top to 
bottom and back to top to verify acceptable 
performance. 



to be placed in the area of the structure, slope stability, 
subsurface drainage, settlement control, and pile, require- 
ments. Except as specifically noted, the term "pile" as used 
in Sections 9.7.4.4 and 9.7.5.4 includes foundation piers, 
caissons, and piles, and the term "pile cap" includes the ele- 
ments to which piles are connected, including grade beams 
and mats. 

9.7.2 Seismic Design Category A. There are no special 
requirements for the foundations of structures assigned to 
Category A. 

9.7.3 Seismic Design Category B. The determination of 
the site coefficient, Section 9.4,1.2.4, shall be documented 
and the resisting capacities of the foundations, subjected to 
the prescribed seismic forces of Sections 9.1 through 9.9, 
shall meet the following requirements. 

9.7.3.1 Structural Components. The design strength 
of foundation components subjected to seismic forces 
alone or in combination with other prescribed loads 
and their detailing requirements shall conform to the 
requirements of Sections 9.8 through 9.12. The strength 
of foundation components shall not be less than that 
required for forces acting without seismic forces. 

9.7.3.2 Soil Capacities. The capacity of the foundation 
soil in bearing, or the capacity of the soil interface 
between pile or pier and the soil, shall be sufficient to 
support the structure with all prescribed loads, without 
seismic forces, taking due account of the settlement that 
the structure can withstand. For the load combination, 
including earthquake as specified in Section 9.5.2.7, 
the soil capacities must be sufficient to resist loads at 
acceptable strains considering both the short duration of 
loading and the dynamic properties of the soil. 

9.7.4 Seismic Design Category C. Foundations for struc- 
tures assigned to Category C shall conform to all of the 
requirements for Categories A and B and to the additional 
requirements of this Section. 



9.63.16.5 Retainer Plates. Retainer plates are 
required at the top and bottom of the car and 
counterweight. 



SECTION 9.7 
FOUNDATION DESIGN REQUIREMENTS 

9.7.1 General. This Section includes only those founda- 
tion requirements that are specifically related to seismic- 
resistant construction. It assumes compliance with other 
basic requirements, which include, but are not limited to, 
the extent of the foundation investigation, fills present or 



9.7.4.1 Investigation. When required by the authority 
having jurisdiction, a written geotechnical or geologic 
report shall be submitted. This report shall include, 
in addition to the requirements of Section 9.7,1 and 
the evaluations required in Section 9.7.3, the results 
of an investigation to evaluate the following potential 
earthquake hazards: 

1. Slope instability 

2. Liquefaction 

3. Lateral spreading 

4. Surface rupture 



172 



ASCE 7-02 



The investigation shall contain recommendations for 
appropriate foundation designs or other measures to 
mitigate the effects of the above hazards. 

9.7.4.2 Pole-Type Structures. When construction emp- 
loying posts or poles as columns embedded in earth or 
embedded in concrete footings in the earth is used to 
resist lateral loads, the depth of embedment required 
for posts or poles to resist seismic forces shall be 
determined by means of the design criteria established 
in the foundation investigation report. 

9.7.43 Foundation Ties. Individual pile caps, drilled 
piers, or caissons shall be interconnected by ties. All ties 
shall have a design strength in tension or compression 
greater than a force equal to 10% of S DS times the 
larger pile cap or column factored dead plus factored live 
load unless it is demonstrated that equivalent restraint 
will be provided by reinforced concrete beams within 
slabs on grade or reinforced concrete slabs on grade 
or confinement by competent rock, hard cohesive soils, 
very dense granular soils, or other approved means. 

9.7.4.4 Special Pile Requirements. Concrete piles, 
concrete-filled steel pipe piles, drilled piers, or 
caissons require minimum bending, shear, tension, and 
elastic strain capacities. Refer to Section A. 9. 7.4.4 for 
supplementary provisions. 



9.7.53 Liquefaction Potential and Soil Strength 
Loss. The geotechnical report required by Section 
9.7.5.1 shall assess potential consequences of lique- 
faction and soil strength loss, including estimation of 
differential settlement, lateral movement or reduction 
in foundation soil-bearing capacity, and shall discuss 
mitigation measures. Such measures shall be given 
consideration in the design of the structure and can 
include, but are not limited to, ground stabilization, 
selection of appropriate foundation type and depths, 
selection of appropriate structural systems to accommo- 
date anticipated displacements, or any combination of 
these measures. The potential for liquefaction shall be 
evaluated for site peak ground accelerations, magnitudes, 
and source characteristics consistent with the design 
earthquake ground motions defined in Section 9.4.1.3.4. 
Where deemed appropriate by the authority having juris- 
diction, a site-specific geotechnical report is not required 
when prior evaluations of nearby sites with similar soil 
conditions provide sufficient direction relative to the pro- 
posed construction. 

The potential for liquefaction and soil strength loss 
shall be evaluated for site peak ground accelerations, 
magnitudes, and source characteristics consistent with 
the design earthquake ground motions. Peak ground 
acceleration may be determined based on a site- specific 
study taking into account soil amplification effects or, in 
the absence of such a study, peak ground accelerations 
shall be assumed equal to S s /2.5. 



9.7*5 Foundation Requirements for Seismic Design Cat- 
egories D, E, and F. Foundations for structures assigned 
to Seismic Design Categories D, E, and F shall conform 
to all of the requirements for Seismic Design Category 
C construction and to the additional requirements of this 
Section. Design and construction of concrete foundation 
components shall conform to the requirements of Ref. 9.9- 
1, Section 21.8, except as modified by the requirements of 
this Section. 

Exception: Detached 1- and 2-family dwellings of light- 
frame construction not exceeding 2 stories in height 
above grade need only comply with the requirements 
for Sections 9.7.4 and 9.7.5.3. 

9.7.5.1 Investigation. The owner shall submit to the 
authority having jurisdiction a written report that includes 
an evaluation of the items in Section 9.7.4.1 and the deter- 
mination of lateral pressures on basement and retaining 
walls due to earthquake motions. 

9.7.5.2 Foundation Ties. Individual spread footings 
founded on soil defined in Section 9.4.1.2.1 as Site 
Class E or F shall be interconnected by ties. Ties shall 
conform to Section 9.7.4.3. 



9.7.5.4 Special Pile and Grade Beam Requirements. 
Piling shall be designed and constructed to withstand 
maximum imposed curvatures from earthquake ground 
motions and structure response. Curvatures shall include 
free-field soil strains (without the structure) modified for 
soil-pile-structure interaction coupled with pile defor- 
mations induced by lateral pile resistance to struc- 
ture seismic forces. Concrete piles in Site Class E or 
F shall be designed and detailed in accordance with 
Sections 21.4.4.1, 21.4.4.2, and 21.4.4.3 of Ref. 9.9-1 
within seven pile diameters of the pile cap and the inter- 
faces of soft to medium stiff clay or liquefiable strata. 
Refer to Section A.9.7.5 for supplementary provisions in 
addition to those given in Section A. 9. 7.4.4. Batter piles 
and their connections shall be capable of resisting forces 
and moments from the special seismic load combinations 
of Section 9.5.2.7.1. For precast, prestressed concrete 
piles, detailing provisions as given in Section A.9.7.5. 4.4 
shall apply. 

Section 21.8.3.3 of Ref. 9.9-1 need not apply when 
grade beams have the required strength to resist the 
forces from the special seismic loads of Section 9.5.2.7.1. 
Section 21.8.4.4(a) of Ref. 9.9-1 need not apply to con- 
crete piles. Section 21.8.4.4(b) ofACI 318 need not apply 
to precast, prestressed concrete piles. 



Minimum Design Loads for Buildings and Other Structures 



173 



Design of anchorage of piles into the pile cap shall 
consider the combined effect of axial forces due to uplift 
and bending moments due to fixity to the pile cap. For 
piles required to resist uplift forces or provide rotational 
restraint, anchorage into the pile cap shall be capable of 
developing the following: 

1. In the case of uplift, the lesser of the nominal 
tensile strength of the longitudinal reinforcement 
in a concrete pile, or the nominal tensile strength of 
a steel pile, or 1.3 times the pile pullout resistance, 
or the axial tension force resulting from the special 
seismic loads of Section 9.5.2.7.1. 

2. In the case of rotational restraint, the lesser of the 
axial and shear forces and moments resulting from 
the special seismic loads of Section 9.5.2.7.1 or 
development of the full axial, bending, and shear 
nominal strength of the pile. 

Splices of pile segments shall develop the nominal 
strength of the pile section, but the splice need not 
develop the nominal strength of the pile in tension, shear, 
and bending when it has been designed to resist axial and 
shear forces and moments from the special seismic loads 
of Section 9.5.2.7.1. 

Pile moments, shears, and lateral deflections used for 
design shall be established considering the interaction 
of the shaft and soil. Where the ratio of the depth of 
embedment of the pile-to-the-pile diameter or width is 
less than or equal to 6, the pile may be assumed to be 
flexuraily rigid with respect to the soil. 

Pile group effects from soil on lateral pile nominal 
strength shall be included where pile center-to-center 
spacing in the direction of lateral force is less than eight 
pile diameters or widths. Pile group effects on vertical 
nominal strength shall be included where pile center-to- 
center spacing is less than three pile diameters or widths. 



Design Specification for Structural Steel 
Buildings (ASD), June 1, 1989. 

Reference 9.8-3 American Institute of Steel Construction, 
Seismic Provisions for Structural Steel 
Buildings, Parti, 1997, including Sup- 
plement 2, November 10, 2000. 

Reference 9.8-4 American Iron and Steel Institute 
(AISI), Specification for the Design of 
Cold-Formed Steel Structural Members, 
1996, including Supplement No. 1, July 
30, 1999. 

Reference 9.8-5 ASCE, Specification for the Design of 
Cold-Formed Stainless Steel Structural 
Members, ASCE 8-90, 1990. 

Reference 9.8-6 Steel Joist Institute, Standard Specifica- 
tion, Load Tables and Weight Tables for 
Steel Joists and joist Girders, 1 994. 

Reference 9.8-7 ASCE, Structured Applications for Steel 
Cables for Buildings, ASCE 19-95, 1995. 



SECTION 9.9 
STRUCTURAL CONCRETE 

9.9.1 Reference Documents. The quality and testing of 
materials and the design and construction of structural con- 
crete components that resist seismic forces shall conform 
to the requirements of the references listed in this Section 
except that modifications are necessary to make the ref- 
erence compatible with the provisions of this document. 
Appendix A. 9. 9 provides the supplementary provisions for 
this compatibility. The load combinations of Section 2.4.1 
are not applicable for design of reinforced concrete to resist 
earthquake loads. 

Reference 9.9-1 American Concrete Institute, Building 
Code Requirements for Structural Con- 
crete, ACI 318-02. 



SECTION 9.8 
STEEL 

9,8.1 Reference Documents. The design, construction, 
and quality of steel components that resist seismic forces 
shall conform to the requirements of the references listed in 
this Section except that modifications are necessary to make 
the references compatible with the provisions of this doc- 
ument. Appendix A. 9. 8 provides supplementary provisions 
for this compatibility. 

Reference 9.8-1 American Institute of Steel Construc- 
tion (AISC), Load and Resistance Factor 
Design Specification for Structural Steel 
Buildings (LRFD), 1999. 

Reference 9.8-2 American Institute of Steel Construc- 
tion, Allowable Stress Design and Plastic 



SECTION 9.10 
COMPOSITE STRUCTURES 

9.10.1 Reference Documents. The design, construction, 
and quality of composite steel and concrete components 
that resist seismic forces shall conform to the relevant 
requirements of the following references except as modified 
by the provisions of this chapter. 

Reference 9.10-1 American Institute of Steel Construc- 
tion (AISC), Load and Resistance Fac- 
tor Design Specification for Structural 
Steel Buildings (LRFD), 1999. 

Reference 9.10-2 American Concete Institute (ACI), 
Building Code Requirements for Struc- 
tural Concrete, 1999, excluding 



174 



ASCE 7-02 



Reference 9.10-3 



Reference 9/10-4 



Appendix A, (Alternate Design Method) 
and Chapter 22 (Structural Plain Con- 
crete) and making Appendix C (Alterna- 
tive Load and Strength Reduction Fac- 
tors) mandatory. 

American Institute of Steel Construc- 
tion (AISC), Seismic Provisions for 
Structural Steel Buildings, Including 
Supplement No. 1 (February 15, 1999, 
July 1997, Parts I and II. 
American Iron and Steel Institute 
(AISI), Specification for the Design of 
Cold-Formed Steel Structural Members, 
1996, including Supplement 2000, 
excluding ASD provisions. 



9.10.1.1 When using ACI [2], Appendix A and Chap- 
ter 22 are excluded and Appendix C is mandatory. 

SECTION 9.11 
MASONRY 

9.11.1 Reference Documents. The design, construction, 
and quality assurance of masonry components that resist 
seismic forces shall conform to the requirements of the 
reference listed in this Section except that modifications 
are necessary to make the reference compatible with the 
provisions of this document. Appendix A.9.11 provides the 
supplementary provisions for this compatibility. 



Reference 9.11-1 



American Concrete Institute, Building 
Code Requirements for Masonry Struc- 
tures, ACI 530-99/ASCE 5-99/TMS 
402-99, 1999 and Specifications for 
Masonry Structures, ACI 530.1-99/ 
ASCE 6-99/TMS 602-99, 1999. 



SECTION 9.12 
WOOD 



9.12.1 Reference Documents. The quality, testing, design, 
and construction of members and their fastenings in 
wood systems that resist seismic forces shall conform 
to the requirements of the reference documents listed in 
this Section. 

9.12.1.1 Consensus Standards. 



Reference 9.12-1 



Reference 9.12-2 



National Design Specification for 
Wood Construction, including sup- 
plements, ANSI/AF&PA NDS-2001 
(2001). 

National Institute of Standards and 
Technology, American Softwood 
Lumber Standard, Voluntary Product 
Standard PS 20-99, (1999). 



Reference 9.12-3 
Reference 9.12-4 
Reference 9.12-5 

Reference 9.12-6 

Reference 9.12-7 
Reference 9.12-8 

Reference 9.12-9 



Softwood Plywood- Construction 
and Industrial PS 1-95 (1995). 
ANSI, Wood Particle Board, ANSI 
A208J, (1993). 

Performance Standard for Wood 
Based Structural Use Panels PS 2-92 
(1992). 

American National Standard for 
Wood Products -Structural Glued 
Laminated Timber," ANSI/AITC 
A190.1-1992. 

Wood Poles — Specifications and 
Dimensions ANSI 05.1 (1992). 
Standard Specification for Estab- 
lishing and Monitoring Structural 
Capacities of Prefabricated Wood I- 
Joists, ASTM D 505 5 -95 A (1995). 
Load and Resistance Factor Design 
(LRFD), Standard for Engineered 
Wood Construction, including sup- 
plements, ASCE 16-95 (1995). 



9.12.1.2 Other References. 



Reference 9.12-10 



International Code Council, (ICC) 

2000 International Residential Code 
with the 2002 Supplement, 2000. 



SECTION 9.13 

PROVISIONS FOR SEfStVtfGALLY ISOLATED 

STRUCTURES 

9.13.1 General. Every seismically isolated structure and 
every portion thereof shall be designed and constructed in 
accordance with the requirements of this Section and the 
applicable requirements of Section 9.1. 

The lateral force-resisting system and the isolation 
system shall be designed to resist the deformations and 
stresses produced by the effects of seismic ground motions 
as provided in this Section. 

9.13.2 Criteria Selection. 

9.13.2.1 Basis for Design. The procedures and limita- 
tions for the design of seismically isolated structures 
shall be determined considering zoning, site characteris- 
tics, vertical acceleration, cracked section properties of 
concrete and masonry members, Seismic Use Group, 
configuration, structural system, and height in accor- 
dance with Section 9.5.2 except as noted below. 

9.13.2.2 Stability of the Isolation System. The stabil- 
ity of the vertical load-carrying elements of the isolation 
system shall be verified by analysis and test, as required, 
for lateral seismic displacement equal to the total maxi- 
mum displacement. 



Minimum Design Loads for Buildings and Other Structures 



175 



9.13.2.3 Seismic Use Group. All portions of the struc- 
ture, including the structure above the isolation system, 
shall be assigned a Seismic Use Group in accordance 
with the requirements of Section 9.1.3. The Occupancy 
Importance Factor shall be taken as 1.0 for a seismically 
isolated structure, regardless of its Seismic Use Group 
categorization. 

9.13.2.4 Configuration Requirements. Each structure 
shall be designated as being regular or irregular on 
the basis of the structural configuration above the 
isolation system. 

9.13.2.5 Selection of Lateral Response Procedure. 

9.13.2.5.1 General. Seismically isolated structures 
except those defined in Section 9.13.2.5.2 shall be 
designed using the dynamic lateral response proce- 
dure of Section 9.13.4. 

9.13.2.5.2 Equivalent Lateral Force Procedure. 
The equivalent lateral response procedure of Section 
9.13.3 is permitted to be used for design of a seismi- 
cally isolated structure provided that: 

1. The structure is located at a site with S\ less 
than or equal to 0.60 g. 

2. The structure is located on a Class A, B, C, or 
D site. 

3. The structure above the isolation interface is 
less than or equal to 4 stories or 65 ft (19.8 m) 
in height. 

4. The effective period of the isolated structure 
at maximum displacement, T M , is less than or 
equal to 3.0 sec. 

5. The effective period of the isolated structure 
at the design displacement, T D , is greater than 
three times the elastic, fixed-base period of 
the structure above the isolation system as 
determined by Eq. 9.5.3.3-1 or 9.5.3.3-2. 

6. The structure above the isolation system is of 
regular configuration. 

7. The isolation system meets all of the follow- 
ing criteria: 

a. The effective stiffness of the isolation system 
at the design displacement is greater than 
one-third of the effective stiffness at 20% of 
the design displacement. 

b. The isolation system is capable of pro- 
ducing a restoring force as specified in 
Section 9.13.6.2.4. 

c. The isolation system has force-deflection 
properties that are independent of the rate 
of loading. 



d. The isolation system has force-deflection 
properties that are independent of vertical 
load and bilateral load. 

e. The isolation system does not limit maxi- 
mum considered earthquake displacement to 
less than Smi/Soi times the total design dis- 
placement. 

9.13.2.5.3 Dynamic Analysis. The dynamic lateral 
response procedure of Section 9.13.4 shall be used as 
specified below. 

9.13.2.5.3.1 Response-Spectrum Analysis. Res- 
ponse-spectrum analysis shall not be used for 
design of a seismically isolated structure unless: 

1. The structure is located on a Class A, B, C, 
or D Site 

2. The isolation system meets the criteria of 
Item 7 of Section 9.13.2.5.2. 

9.13.2.5.3.2 Time-History Analysis. Time-history 
analysis shall be permitted for design of any seis- 
mically isolated structure and shall be used for 
design of all seismically isolated structures not 
meeting the criteria of Section 9.13.2.5.3.1. 

9.13.2.5.3.3 Site-Specific Design Spectra. Site- 
specific ground-motion spectra of the design earth- 
quake and the maximum considered earthquake 
developed in accordance with Section 9.13.4.4.1 
shall be used for design and analysis of all seismi- 
cally isolated structures if any one of the following 
conditions apply: 

1. The structure is located on a Class F Site 

2. The structure is located at a site with 
S\ greater than 0.60 g, as determined in 
Section 9.4.1. 



9.13.3 Equivalent Lateral Force Procedure. 

9.13.3.1 General. Except as provided in Section 9.13.4, 
every seismically isolated structure or portion thereof 
shall be designed and constructed to resist minimum 
earthquake displacements and forces as specified by this 
Section and the applicable requirements of Section 9.5.3. 

9.13.3.2 Deformation Characteristics of the Isolation 
System. Minimum lateral earthquake design displace- 
ments and forces on seismically isolated structures shall 
be based on the deformation characteristics of the isola- 
tion system. 



176 



ASCE 7-02 



The deformation characteristics of the isolation sys- 
tem shall explicitly include the effects of the wind- 
restraint system if such a system is used to meet the 
design requirements of this document. 

The deformation characteristics of the isolation sys- 
tem shall be based on properly substantiated tests per- 
formed in accordance with Section 9.13.9. 

9.13.33 Minimum Lateral Displacements. 

9.13.3.3.1 Design Displacement. The isolation sys- 
tem shall be designed and constructed to withstand 
minimum lateral earthquake displacements, D D , that 
act in the direction of each of the main horizontal axes 
of the structure in accordance with the following: 



Dn = 



where 



gSp\T D 
4ti 2 B d 



(Eq. 9.13.3.3.1) 



g = acceleration of gravity. The units of the 
acceleration of gravity, g, are in. /sec 2 
(mm/sec 2 ) if the units of the design 
displacement, Z), are in. (mm) 
S D i = design 5% damped spectral acceleration at 

1-sec period, in units of g-sec, as determined 
in Section 9.4.1.1 

T D — effective period of seismically isolated 
structure in seconds (sec), at the design 
displacement in the direction under 
consideration, as prescribed by Eq. 9.13.3.3.2 

B D — numerical coefficient related to the effective 
damping of the isolation system at the design 
displacement, D D , as set forth in 
Table 9.13.3.3.1 

TABLE 9.13.3.3.1 
DAMPING COEFFICIENT, B/ 



Effective Damping, 

#D or $M 
(Percentage of Critical) 3 '* 3 


B D or B M Factor 


<2% 


0.8 


5% 


1.0 


10% 


1.2 


20% 


1.5 


30% 


1.7 


40% 


1.9 


>50% 


2.0 



a The damping coefficient shall be based on the effective 
damping of the isolation system determined in accor- 
dance with the requirements of Section 9.13.9.5.2. 
b The damping coefficient shall be based on linear 
interpolation for effective damping values other than 
those given. 



9.1333.2 Effective Period at Design Displacement 
The effective period of the isolated structure at design 
displacement, To, shall be determined using the 
deformational characteristics of the isolation system 
in accordance with the following equation: 



T D - 2jr 



W 



kDming 



(Eq. 9.133.3.2) 



where 



W = total seismic dead load weight of the 
structure above the isolation interface as 
defined in Section 9.5.3 (kip or kN) 
komin — minimum effective stiffness in 

kips/in.(kN/mm) of the isolation system at 
the design displacement in the horizontal 
direction under consideration as prescribed 
by Eq. 9.13.9.5.1-2 
g = acceleration due to gravity 

9.13333 Maximum Lateral Displacement The 
maximum displacement of the isolation system, D M , 
in the most critical direction of horizontal response 
shall be calculated in accordance with the formula: 



Dm = 



g$M\T] 



M 



An 2 Bx 



(Eq. 9.13333) 



where 



g — acceleration of gravity 
Sm\ = maximum considered 5% damped spectral 
acceleration at 1-sec period, in units of 
g-sec, as determined in Section 9.4.1.2 

T M — effective period, in seconds (sec), of 

seismic-isolated structure at the maximum 
displacement in the direction under 
consideration as prescribed by Eq. 9.13.3.3.4 

B M = numerical coefficient related to the effective 
damping of the isolation system at the 
maximum displacement, D m , as set forth in 
Table 9.13.3.3.1 

9.13.3.3.4 Effective Period at Maximum Displace- 
ment. The effective period of the isolated structure 
at maximum displacement, 7^, shall be determined 
using the deformational characteristics of the isolation 
system in accordance with the equation: 



T M = In 



W 



(Eq. 9.1333.4) 



^Mmit 



where 

W = 



total seismic dead load weight of the 
structure above the isolation interface as 



Minimum Design Loads for Buildings and Other Structures 



177 



defined in Sections 9.5.3.2 and 9.5.5.3 
(kip or kN) 
kMmin ~ minimum effective stiffness, in kips/in. 
(kN/mm), of the isolation system at the 
maximum displacement in the horizontal 
direction under consideration as prescribed 
by Eq. 9.1.3.9.5.1-4 
g = acceleration of gravity 



9.1333.5 Total Lateral Displacement. The total 
design displacement, D TD , and the total maximum 
displacement, D TM , of elements of the isolation sys- 
tem shall include additional displacement due to 
actual and accidental torsion calculated from the spa- 
tial distribution of the lateral stiffness of the isolation 
system and the most disadvantageous location of mass 
eccentricity. 

The total design displacement, D TD , and the total 
maximum displacement, D TM , of elements of an 
isolation system with uniform spatial distribution of 
lateral stiffness shall not be taken as less than that 
prescribed by the following equations: 



Dtd — &D 



1 + ? 

i + y 



lie 



b 2 + d 2 _ 

lie 
b 2 + d 2 



(Eq. 9.1333.5-1) 
(Eq. 9.1333.5-2) 



Exception: The total design displacement, D TD , 
and the total maximum displacement, Djm> are 
permitted to be taken as less than the value 
prescribed by Eqs. 9.13.3.3.5-1 and 9.13.33.5-2, 
respectively, but not less than 1.1 times D D and 
Dm, respectively, provided the isolation system is 
shown by calculation to be configured to resist 
torsion accordingly. 

where 

D D = design displacement, in in. (mm), at the 

center of rigidity of the isolation system in 
the direction under consideration as 
prescribed by Eq. 9.13.3.3.1 

D M ~ maximum displacement, in in. (mm), at the 
center of rigidity of the isolation system in 
the direction under consideration as 
prescribed by Eq. 9.13.3.3.3 
y = the distance, in ft (mm), between the centers 
of rigidity of the isolation system and the 
element of interest measured perpendicular to 
the direction of seismic loading under 
consideration 
e — the actual eccentricity, in ft (mm), measured 
in plan between the center of mass of the 
structure above the isolation interface and the 



center of rigidity of the isolation system, plus 
accidental eccentricity, in ft (mm), taken as 
5% of the longest plan dimension of the 
structure perpendicular to the direction of 
force under consideration 

b = the shortest plan dimension of the structure, 
in ft (mm), measured perpendicular to d 

d — the longest plan dimension of the structure, 
in ft (mm) 

9.133.4 Minimum Lateral Forces. 

9.133.4.1 Isolation System and Structural Ele- 
ments at or Below the Isolation System. 

The isolation system, the foundation, and all struc- 
tural elements below the isolation system shall be 
designed and constructed to withstand a minimum 
lateral seismic force, Vfc, using all of the appropriate 
provisions for a nonisolated structure where 



V b =K 



DmaxDo 



(Eq. 9.133.4.1) 



where 



y b = the minimum lateral seismic design force 
or shear on elements of the isolation 
system or elements below the isolation 
system as prescribed by Eq. 9.13.3.4.1 
komax = maximum effective stiffness, in kips/in. 
(kN/mm), of the isolation system at the 
design displacement in the horizontal 
direction under consideration 
D D — design displacement, in in. (mm), at the 

center of rigidity of the isolation system in 
the direction under consideration as 
prescribed by Eq. 9.1333.1 

Vjy shall not be taken as less than the maximum force 
in the isolation system at any displacement up to and 
including the design displacement. 

9.133.4.2 Structural Elements Above the Isolation 
System. The structure above the isolation system shall 
be designed and constructed to withstand a minimum 
shear force, V s , using all of the appropriate provisions 
for a nonisolated structure where 



V« = 



^Dmax 



xD D 



(Eq. 9.133.4.2) 



where 



komax = maximum effective stiffness, in kips/in. 
(kN/mm), of the isolation system at the 
design displacement in the horizontal 
direction under consideration 



178 



ASCE 7-02 



Do = design displacement in in. (mm), at the 

center of rigidity of the isolation system in 
the direction under consideration as 
prescribed by Eq. 9.13.3.3.1 
Rf — numerical coefficient related to the type of 
lateral force-resisting system above the 
isolation system 

The Rj factor shall be based on the type of lateral- 
force-resisting system used for the structure above 
the isolation system and shall be three-eighths of the 
R value given in Table 9.5.2.2 with an upper-bound 
value not to exceed 2.0 and a lower bound value not 
to be less than 1.0. 

9.13.3.4.3 Limits on V,. The value of V s shall not 
be taken as less than the following: 

1. The lateral seismic force required by Sec- 
tion 9.5.3 for a fixed-base structure of the same 
weight, W, and a period equal to the isolated 
period, To, 

2. The base shear corresponding to the factored 
design wind load. 

3. The lateral seismic force required to fully acti- 
vate the isolation system (e.g., the yield level 
of a softening system, the ultimate capacity of 
a sacrificial wind-restraint system, or the break- 
away friction level of a sliding system) factored 
by 1.5. 

9.13.3.5 Vertical Distribution of Force. The total force 
shall be distributed over the height of the structure above 
the isolation interface in accordance with the follow- 
ing equation: 



F x = 



V S W X h x 



(Eq. 9.13.3.5) 



^wthi 



where 



i=i 



V s = total lateral seismic design force or shear on 

elements above the isolation system as 

prescribed by Eq. 9.13.3.4.2 
W x = portion of W that is located at or assigned to 

Level z, n, or x, respectively 
h x = height above the base Level /, n, or x, 

respectively 
Wi = portion of W that is located at or assigned to 

Level i, n, on, respectively 
hi = height above the base Level z, n, or x, 

respectively 

At each level designated as x, the force, F x , shall be 
applied over the area of the structure in accordance with 



the mass distribution at the level. Stresses in each struc- 
tural element shall be calculated as the effect of force, 
F X7 applied at the appropriate levels above the base. 

9.13.3.6 Drift Limits. The maximum interstory drift of 
the structure above the isolation system shall not exceed 
0.0\5h sx . The drift shall be calculated by Eq. 9.5.3.7.1 
with the Cd factor of the isolated structure equal to the 
Ri factor defined in Section 9.13.3.4.2. 

9.13.4 Dynamic Lateral Response Procedure. 

9.13.4.1 General. As required by Section 9.13.2, every 
seismically isolated structure or portion thereof shall be 
designed and constructed to resist earthquake displace- 
ments and forces as specified in this Section and the 
applicable requirements of Section 9.5.4. 

9.13.4.2 Isolation System and Structural Elements 
Below the Isolation System. The total design displace- 
ment of the isolation system shall not be taken as less 
than 90% of D TD as specified by Section 9.13.3.3.5. 

The total maximum displacement of the isolation 
system shall not be taken as less than 80% of D TM as 
prescribed by Section 9.13.3.3.5. 

The design lateral shear force on the isolation system 
and structural elements below the isolation system shall 
not be taken as less than 90% of Vt> as prescribed by 
Eq. 9.13.3.4.1. 

The limits on displacements specified by this Section 
shall be evaluated using values of Dtd an d &tm 
determined in accordance with Section 9.13.3.5 except 
that D D > is permitted to be used in lieu of D D and D M * 
is permitted to be used in lieu of Dm where 



D' 



& M = 



D f 



/i + (T/r D ) 2 

Dm 

J\ + (T/T M ) 2 



(Eq. 9.13.4.2-1) 
(Eq. 9.13.4.2-2) 



where 



D D — design displacement, in in. (mm), at the 

center of rigidity of the isolation system in 
the direction under consideration as 
prescribed by Eq. 9.13.3.3.1 

D M = maximum displacement in in. (mm), at the 
center of rigidity of the isolation system in 
the direction under consideration as 
prescribed by Eq. 9.13.3.3.3 
T = elastic, fixed-base period of the structure 
above the isolation system as determined by 
Section 9.5.3.3 

T D = effective period of seismically isolated 

structure in sec, at the design displacement 



Minimum Design Loads for Buildings and Other Structures 



179 



in the direction under consideration as 
prescribed by Eq. 9.13.3.3.2 
T M = effective period, in sec, of the seismically 
isolated structure, at the maximum 
displacement in the direction under 
consideration as prescribed by Eq. 9.13.3.3.4 

9.13.4.3 Structural Elements Above the Isolation 
System. The design lateral shear force on the structure 
above the isolation system, if regular in configuration, 
shall not be taken as less than 80% of V s , or less than 
the limits specified by Section 9.13.3.4.3. 

Exception: The design lateral shear force on the 
structure above the isolation system, if regular in 
configuration, is permitted to be taken as less than 
80%, but shall not be less than 60% of V s , when time- 
history analysis is used for design of the structure. 

The design lateral shear force on the structure above the 
isolation system, if irregular in configuration, shall not 
be taken as less than V s , or less than the limits specified 
by Section 9.13.3.4.3. 

Exception: The design lateral shear force on the 
structure above the isolation system, if irregular 
in configuration, is permitted to be taken as less 
than 100%, but shall not be less than 80% of V s , 
when time-history analysis is used for design of 
the structure. 

9.13.4.4 Ground Motion. 

9.13.4.4.1 Design Spectra. Properly substantiated 
site- specific spectra are required for design of all 
structures located on Site Class E or F or located at 
a site with S\ greater than 0.60 g. Structures that do 
not require site-specific spectra and for which site- 
specific spectra have not been calculated shall be 
designed using the response spectrum shape given in 
Figure 9.4.1.2.6. 

A design spectrum shall be constructed for the 
design earthquake. This design spectrum shall not 
be taken as less than the design earthquake response 
spectrum given in Figure 9.4.1.2.6. 

Exception: If a site-specific spectrum is calculated 
for the design earthquake, the design spectrum is 
permitted to be taken as less than 100% but shall 
not be less than 80% of the design earthquake 
response spectrum given in Figure 9.4.1.2.6. 

A design spectrum shall be constructed for the 
maximum considered earthquake. This design spec- 
trum shall not be taken as less than 1.5 times 
the design earthquake response spectrum given in 



Figure 9.4.1.2.6. This design spectrum shall be used 
to determine the total maximum displacement and 
overturning forces for design and testing of the isola- 
tion system. 

Exception: If a site- specific spectrum is calcu- 
lated for the maximum considered earthquake, the 
design spectrum is permitted to be taken as less 
than 100% but shall not be less than 80% of 
1.5 times the design earthquake response spectrum 
given in Figure 9.4.1.2.6. 

9.13.4.4.2 Time Histories. Pairs of horizontal 
ground-motion time-history components shall be 
selected and scaled from not less than three recorded 
events. For each pair of horizontal ground-motion 
components, the square root sum of the squares 
(SRSS) of the 5% damped spectrum of the scaled, 
horizontal components shall be constructed. The 
motions shall be scaled such that the average value 
of the SRSS spectra does not fall below 1.3 times the 
5% damped spectrum of the design earthquake (or 
maximum considered earthquake) by more than 10% 
for periods from 0.5 T D seconds to 1 .25 Tm seconds 
where Tp and Tm are determined in accordance with 
Sections 9.13.3.3.2 and 9.13.3.3.4, respectively. 

9.13.4.5 Mathematical Model. 

9.13.4.5.1 General. The mathematical models of 
the isolated structure including the isolation sys- 
tem, the lateral -force-resisting system, and other 
structural elements shall conform to Section 9.5.4.2 
and to the requirements of Sections 9.13.4.5.2 and 
9.13.4.5.3, below. 

9.13.4.5.2 Isolation System. The isolation system 
shall be modeled using deformational characteristics 
developed and verified by test in accordance with 
the requirements of Section 9.13.3.2. The isolation 
system shall be modeled with sufficient detail to: 

1. Account for the spatial distribution of isola- 
tor units. 

2. Calculate translation, in both horizontal direc- 
tions, and torsion of the structure above the 
isolation interface considering the most disad- 
vantageous location of mass eccentricity. 

3. Assess overturning/uplift forces on individual 
isolator units. 

4. Account for the effects of vertical load, bilateral 
load, and/or the rate of loading if the force- 
deflection properties of the isolation system are 
dependent on one or more of these attributes. 



180 



ASCE 7-02 



9.13.4.53 Isolated Building. 

9.13.4.5.3.1 Displacement. The maximum dis- 
placement of each floor and the total design dis- 
placement and total maximum displacement across 
the isolation system shall be calculated using a 
model of the isolated structure that incorporates the 
force-deflection characteristics of nonlinear ele- 
ments of the isolation system and the lateral-force- 
resisting system. 

Isolation systems with nonlinear elements 
include, but are not limited to, systems that do not 
meet the criteria of Item 7 of Section 9.13.2.5.2. 

Lateral-force-resisting systems with nonlinear 
elements include, but are not limited to, irregular 
structural systems designed for a lateral force less 
than V s and regular structural systems designed for 
a lateral force less than 80% of V s . 

9.13.4.5.3.2 Forces and Displacements in Key 
Elements. Design forces and displacements in key 
elements of the lateral-force-resisting system shall 
not be calculated using a linear elastic model of 
the isolated structure unless: 

1. Pseudo-elastic properties assumed for non- 
linear isolation system components are based 
on the maximum effective stiffness of the 
isolation system. 

2. All key elements of the lateral-force-resisting 
system are linear. 

9.13.4.6 Description of Analysis Procedures. 

9.13.4.6.1 General. Response-spectrum and time- 
history analyses shall be performed in accordance 
with Section 9.5.3 and the requirements of this 
section. 

9.13.4.6.2 Input Earthquake. The design earth- 
quake shall be used to calculate the total design 
displacement of the isolation system and the lateral 
forces and displacements of the isolated structure. 
The maximum considered earthquake shall be used 
to calculate the total maximum displacement of the 
isolation system. 



the model by 100% of the most critical direction of 
ground motion and 30% of the ground motion on the 
orthogonal axis. The maximum displacement of the 
isolation system shall be calculated as the vectorial 
sum of the two orthogonal displacements. 

The design shear at any story shall not be less 
than the story shear obtained using Eq. 9.13.3.5 and 
a value of V s taken as that equal to the base shear 
obtained from the response-spectrum analysis in the 
direction of interest. 

9.13.4.6.4 Time-History Analysis. Time-history ana- 
lysis shall be performed with at least three appro- 
priate pairs of horizontal time-history components as 
defined in Section 9.13.4.4.2. 

Each pair of time histories shall be applied simulta- 
neously to the model considering the most disadvan- 
tageous location of mass eccentricity. The maximum 
displacement of the isolation system shall be calcu- 
lated from the vectorial sum of the two orthogonal 
components at each time step. 

The parameter of interest shall be calculated for 
each time-history analysis. If three time-history anal- 
yses are performed, the maximum response of the 
parameter of interest shall be used for design. If seven 
or more time-history analyses are performed, the aver- 
age value of the response parameter of interest shall 
be used for design. 

9.13.4.7 Design Lateral Force. 

9.13.4.7.1 Isolation System and Structural Ele- 
ments at or Below the Isolation System. The iso- 
lation system, foundation, and all structural elements 
below the isolation system shall be designed using 
all of the appropriate provisions for a nonisolated 
structure and the forces obtained from the dynamic 
analysis without reduction. 

9.13.4.7.2 Structural Elements Above the Isolation 

System. Structural elements above the isolation sys- 
tem shall be designed using the appropriate provisions 
for a nonisolated structure and the forces obtained 
from the dynamic analysis reduced by a factor of Rj. 
The Rf factor shall be based on the type of lateral- 
force-resisting system used for the structure above the 
isolation system. 



9.13.4.6.3 Response-Spectrum Analysis. Response- 
spectrum analysis shall be performed using a damping 
value equal to the effective damping of the isolation 
system or 30% of critical, whichever is less. 

Response-spectrum analysis used to determine the 
total design displacement and the total maximum 
displacement shall include simultaneous excitation of 



9.13.4.7.3 Scaling of Results. When the factored lat- 
eral shear force on structural elements, determined 
using either response-spectrum or time-history anal- 
ysis, is less than the minimum level prescribed by 
Sections 9.13.4.2 and 9.13.4.3, all response parame- 
ters, including member forces and moments, shall be 
adjusted upward proportionally. 



Minimum Design Loads for Buildings and Other Structures 



181 



9.13.4.7.4 Drift Limits. Maximum interstory drift 
corresponding to the design lateral force including 
displacement due to vertical deformation of the iso- 
lation system shall not exceed the following limits: 

1. The maximum interstory drift of the structure 
above the isolation system calculated by 
response-spectrum analysis shall not exceed 
0.015h sx . 

2. The maximum interstory drift of the struc- 
ture above the isolation system calculated 
by time-history analysis based on the force- 
deflection characteristics of nonlinear elements 
of the lateral-force-resisting system shall not 
exceed Q.020h sx . 

Drift shall be calculated using Eq. 9.5.3.7.1 with 
the Cd factor of the isolated structure equal to the Rj 
factor defined in Section 9.13.3.4.2. 

The secondary effects of the maximum considered 
earthquake lateral displacement A of the structure 
above the isolation system combined with gravity 
forces shall be investigated if the interstory drift ratio 
exceeds 0.010//?/. 

9.13.5 Lateral Load on Elements of Structures and 
Nonstructural Components Supported by Buildings. 

9.13.5.1 General. Parts or portions of an isolated 
structure, permanent nonstructural components and the 
attachments to them, and the attachments for permanent 
equipment supported by a structure shall be designed 
to resist seismic forces and displacements as prescribed 
by this section and the applicable requirements of 
Section 9.6. 

9.13.5.2 Forces and Displacements. 

9.13.5.2.1 Components at or Above the Isolation 
Interface. Elements of seismically isolated structures 
and nonstructural components, or portions thereof, 
that are at or above the isolation interface shall be 
designed to resist a total lateral seismic force equal 
to the maximum dynamic response of the element or 
component under consideration. 

Exception: Elements of seismically isolated struc- 
tures and nonstructural components or portions 
designed to resist total lateral seismic force as 
prescribed in Sections 9.5.2.6 and 9.6.1.3 as appro- 
priate, 

9.13.5.2.2 Components Crossing the Isolation 

Interface. Elements of seismically isolated structures 
and nonstructural components, or portions thereof, 



that cross the isolation interface shall be designed to 
withstand the total maximum displacement. 

9.13.5.2.3 Components Below the Isolation Inter- 
face. Elements of seismically isolated structure and 
nonstructural components, or portions thereof, that 
are below the isolation interface shall be designed 
and constructed in accordance with the requirements 
of Section 9.5.2. 

9.13.6 Detailed System Requirements. 

9.13.6.1 General. The isolation system and the struc- 
tural system shall comply with the material requirements 
of Sections 9.8 through 9.1.2. In addition, the isolation 
system shall comply with the detailed system require- 
ments of this section and the structural system shall 
comply with the detailed system requirements of this 
section and the applicable portions of Section 9.5.2. 

9.13.6.2 Isolation System. 

9.13.6.2.1 Environmental Conditions. In addition to 
the requirements for vertical and lateral loads induced 
by wind and earthquake, the isolation system shall 
provide for other environmental conditions including 
aging effects, creep, fatigue, operating temperature, 
and exposure to moisture or damaging substances. 

9.13.6.2.2 Wind Forces. Isolated structures shall 
resist design wind loads at all levels above the iso- 
lation interface. At the isolation interface, a wind- 
restraint system shall be provided to limit lateral dis- 
placement in the isolation system to a value equal to 
that required between floors of the structure above the 
isolation interface. 

9.13.6.2.3 Fire Resistance. Fire resistance for the 
isolation system shall meet that required for the struc- 
ture columns, walls, or other such gravity-bearing 
elements in the same area of the structure. 

9.13.6.2.4 Lateral Restoring Force. The isolation 
system shall be configured to produce a restoring 
force such that the lateral force at the total design 
displacement is at least 0.025 W greater than the 
lateral force at 50% of the total design displacement. 

Exception: The isolation system need not be con- 
figured to produce a restoring force, as required 
above, provided the isolation system is capa- 
ble of remaining stable under full vertical load 
and accommodating a total maximum displace- 
ment equal to the greater of either 3.0 times 
the total design displacement or 36Sm\ in. (or 
915S M [ mm). 



182 



ASCE 7-02 



9.13.6.2.5 Displacement Restraint. The isolation 
system shall not be configured to include a displace- 
ment restraint that limits lateral displacement due 
to the maximum considered earthquake to less than 
Sm\I$d\ times the total design displacement unless 
the seismically isolated structure is designed in accor- 
dance with the following criteria when more stringent 
than the requirements of Section 9.13.2: 

1. Maximum considered earthquake response is 
calculated in accordance with the dynamic anal- 
ysis requirements of Section 9.13.4 explicitly 
considering the nonlinear characteristics of the 
isolation system and the structure above the iso- 
lation system. 

2. The ultimate capacity of the isolation sys- 
tem and structural elements below the isola- 
tion system shall exceed the strength and dis- 
placement demands of the maximum consid- 
ered earthquake. 

3. The structure above the isolation system is 
checked for stability and ductility demand of 
the maximum considered earthquake. 

4. The displacement restraint does not become 
effective at a displacement less than 0.75 times 
the total design displacement unless it is demon- 
strated by analysis that earlier engagement does 
not result in unsatisfactory performance. 

9.13.6.2.6 Vertical-Load Stability. Each element of 
the isolation system shall be designed to be stable 
under the design vertical load at a horizontal dis- 
placement equal to the total maximum displacement. 
The design vertical load shall be computed using load 
combination 5 of Section 2.3.2 for the maximum ver- 
tical load and load combination 7 of Section 2.3.2 
for the minimum vertical load. The seismic load E 
is given by Eqs. 9.5.2.7-1 and 9.5.2.7-2 where S DS 
in these equations is replaced by Sms- The vertical 
load due to earthquake, Qe, shall be based on peak 
response due to the maximum considered earthquake. 

9.13.6.2.7 Overturning. The factor of safety against 
global structural overturning at the isolation interface 
shall not be less than 1.0 for required load combi- 
nations. AH gravity and seismic loading conditions 
shall be investigated. Seismic forces for overturning 
calculations shall be based on the maximum consid- 
ered earthquake and W shall be used for the vertical 
restoring force. 

Local uplift of individual elements shall not be 
allowed unless the resulting deflections do not cause 
overstress or instability of the isolator units or other 
structure elements. 



9.13.6.2.8 Inspection and Replacement 

1. Access for inspection and replacement of all 
components of the isolation system shall be 
provided. 

2. A registered design professional shall complete 
a final series of inspections or observations of 
structure separation areas and components that 
cross the isolation interface prior to the issuance 
of the certificate of occupancy for the seismi- 
cally isolated structure. Such inspections and 
observations shall indicate that the conditions 
allow free and unhindered displacement of the 
structure to maximum design levels and that all 
components that cross the isolation interface as 
installed are able to accommodate the stipulated 
displacements. 

3. Seismically isolated structures shall have a peri- 
odic monitoring, inspection, and maintenance 
program for the isolation system established by 
the registered design professional responsible 
for the design of the system. 

4. Remodeling, repair, or retrofitting at the isola- 
tion system interface, including that of compo- 
nents that cross the isolation interface, shall be 
performed under the direction of a registered 
design professional. 

9.13.6.2.9 Quality Control. A quality control testing 
program for isolator units shall be established by the 
engineer responsible for the structural design. 

9.13.6.3 Structural System. 

9.13.6.3.1 Horizontal Distribution of Force. A hor- 
izontal diaphragm or other structural elements shall 
provide continuity above the isolation interface and 
shall have adequate strength and ductility to transmit 
forces (due to nonuniform ground motion) from one 
part of the structure to another. 

9.13.6.3.2 Building Separations. Minimum separa- 
tions between the isolated structure and surrounding 
retaining walls or other fixed obstructions shall not 
be less than the total maximum displacement. 

9.13.6.3.3 Nonbuilding Structures. These shall be 
designed and constructed in accordance with the 
requirements of Section 9.14 using design displace- 
ments and forces calculated in accordance with 
Section 9.13.3 or 9.13.4. 

9.13.7 Foundations. Foundations shall be designed and 
constructed in accordance with the requirements of 



Minimum Design Loads for Buildings and Other Structures 



183 



Section 4 using design forces calculated in accordance with 
Section 9.13.3 or 9.13.4, as appropriate. 

9.13.8 Design and Construction Review. 

9.13.8.1 General. A design review of the isolation 
system and related test programs shall be performed 
by an independent engineering team including persons 
licensed in the appropriate disciplines and experienced in 
seismic analysis methods and the theory and application 
of seismic isolation, 

9.13.8.2 Isolation System. Isolation system design 
review shall include, but not be limited to, the following: 

1. Review of site-specific seismic criteria includ- 
ing the development of site-specific spectra and 
ground-motion time-histories and all other design 
criteria developed specifically for the project. 

2. Review of the preliminary design including the 
determination of the total design displacement of 
the isolation system design displacement and the 
lateral force design level. 

3. Overview and observation of prototype testing 
(Section 9.13.9). 

4. Review of the final design of the entire structural 
system and all supporting analyses. 

5. Review of the isolation system quality control 
testing program (Section 9.13.6.2.9). 

9.13.9 Required Tests of the Isolation System. 

9.13.9.1 General. The deformation characteristics and 
damping values of the isolation system used in the design 
and analysis of seismically isolated structures shall be 
based on tests of a selected sample of the components 
prior to construction as described in this Section. 

The isolation system components to be tested shall 
include the wind-restraint system if such a system is 
used in the design. 

The tests specified in this section are for establishing 
and validating the design properties of the isolation 
system and shall not be considered as satisfying the 
manufacturing quality control tests of Section 9.13.6.2.9. 

9.13.9.2 Prototype Tests, 

9.13.9.2.1 General. Prototype tests shall be per- 
formed separately on two full-size specimens (or sets 
of specimens, as appropriate) of each predominant 
type and size of isolator unit of the isolation system. 
The test specimens shall include the wind-restraint 
system as well as individual isolator units if such 



systems are used in the design. Specimens tested shall 
not be used for construction unless permitted by the 
registered design professional and authority having 
jurisdiction. 

9.13.9.2.2 Record. For each cycle of tests, the force- 
deflection and hysteretic behavior of the test specimen 
shall be recorded. 

9.13.9.2.3 Sequence and Cycles. The following 
sequence of tests shall be performed for the prescribed 
number of cycles at a vertical load equal to the aver- 
age dead load plus one-half the effects due to live 
load on all isolator units of a common type and size: 

1. Twenty fully reversed cycles of loading at 
a lateral force corresponding to the wind 
design force. 

2. Three fully reversed cycles of loading at each 
of the following increments of the total design 
displacement— 0.25 £> D , 0.5D D , l.QD D , and 
1.0 Dm where Do and D M are as determined in 
Sections 9.13.3.3.1 and 9.13.3.3.3, respectively, 
or Section 9.13.4 as appropriate. 

3. Three fully reversed cycles of loading at the 
total maximum displacement, L0D TM . 

4. 30S D \/S DS B Dj but not less than 10, fully 
reversed cycles of loading at 1 .0 times the total 
design displacement, 1.0D TD . 

If an isolator unit is also a vertical- load -carrying 
element, then Item 2 of the sequence of cyclic tests 
specified above shall be performed for two additional 
vertical load cases specified in Section 9.13.6.2.6. 
The load increment due to earthquake overturning, 
Qe, shall be equal to or greater than the peak 
earthquake vertical force response corresponding to 
the test displacement being evaluated. In these tests, 
the combined vertical load shall be taken as the 
typical or average downward force on all isolator 
units of a common type and size. 

9.13.9.2.4 Units Dependent on Loading Rates. If 
the force-deflection properties of the isolator units are 
dependent on the rate of loading, each set of tests 
specified in Section 9.13.9.2.3 shall be performed 
dynamically at a frequency, /, equal to the inverse 
of the effective period, T D . 

If reduced-scale prototype specimens are used to 
quantify rate-dependent properties of isolators, the 
reduced-scale prototype specimens shall be of the 
same type and material and be manufactured with the 
same processes and quality as full-scale prototypes 
and shall be tested at a frequency that represents full- 
scale prototype loading rates. 



184 



ASCE 7-02 



The force-deflection properties of an isolator unit 
shall be considered to be dependent on the rate of 
loading if there is greater than a plus or minus 15% 
difference in the effective stiffness and the effective 
damping at the design displacement when tested at 
a frequency equal to the inverse of the effective 
period of the isolated structure and when tested at any 
frequency in the range of 0. 1 to 2.0 times the inverse 
of the effective period of the isolated structure. 

9.13.9.2.5 Units Dependent on Bilateral Load. If 

the force-deflection properties of the isolator units 
are dependent on bilateral load, the tests specified in 
Sections 9.13.9.2.3 and 9.13.9.2.4 shall be augmented 
to include bilateral load at the following increments 
of the total design displacement: 0.25 and 1.0, 0.50 
and 1.0, 0.75 and 1.0, and 1.0 and 1.0. 

If reduced- scale prototype specimens are used 
to quantify bilateral -load -dependent properties, the 
reduced-scale specimens shall be of the same type and 
material and manufactured with the same processes 
and quality as full-scale prototypes. 

The force-deflection properties of an isolator unit 
shall be considered to be dependent on bilateral 
load if the bilateral and unilateral force- deflection 
properties have greater than a 15% difference in 
effective stiffness at the design displacement. 

9.13.9.2.6 Maximum and Minimum Vertical Load. 

Isolator units that carry vertical load shall be statically 
tested for maximum and minimum downward vertical 
load at the total maximum displacement. In these 
tests, the combined vertical loads shall be taken as 
specified in Section 9.13.6.2.6 on any one isolator 
of a common type and size. The dead load, £>, and 
live load, L, are specified in Section 9.5.2.7. The 
seismic load E is given by Eqs. 9.5.2.7-1 and 9.5.2.7- 
2 where Sds in these equations is replaced by S M s 
and the vertical load, Q E , is based on the peak 
earthquake vertical force response corresponding to 
the maximum considered earthquake. 

9.13.9.2.7 Sacrificial Wind-Restraint Systems. If a 

sacrificial wind-restraint system is to be utilized, the 
ultimate capacity shall be established by test. 

9.13.9.2.8 Testing Similar Units. The prototype tests 
are not required if an isolator unit is of similar size 
and of the same type and material as a prototype 
isolator unit that has been previously tested using the 
specified sequence of tests. 

9.13.9.3 Determination of Force-Deflection Charac- 
teristics. The force-deflection characteristics of the iso- 
lation system shall be based on the cyclic load tests of 
isolator prototypes specified in Section 9.13.9.2. 



The effective stiffness of an isolator unit, k e ff, shall 
be calculated for each cycle of loading as follows: 



K 



€ 



\F+\ + \F- 

IA+I + IA- 



(Eq. 9.13.9.3-1) 



where F + and F~ are the positive and negative forces, 
at A + and A"", respectively. 

As required, the effective damping, fi e ff, of an isolator 
unit shall be calculated for each cycle of loading by 
the equation: 



Peff = 



'■'loop 



7T^(|A+| + |A-|) 



-h2 



(Eq. 9.13.9.3-2) 



where the energy dissipated per cycle of loading, Ei oop , 
and the effective stiffness, k e jf, shall be based on peak 
test displacements of A + and A - . 

9.13.9.4 System Adequacy. The performance of the 
test specimens shall be assessed as adequate if the 
following conditions are satisfied: 

1. For each increment of test displacement specified 
in Item 2 of Section 9.13.9.2.3 and for each 
vertical load case specified in Section 9.13.9.2.3, 
there is no greater than a 15% difference between 
the effective stiffness at each of the three cycles 
of test and the average value of effective stiffness 
for each test specimen. 

2. For each increment of test displacement specified 
in Item 2 of Section 9.13.9.2.3 and for each 
vertical load case specified in Section 9.13.9.2.3, 
there is no greater than a 15% difference in the 
average value of effective stiffness of the two 
test specimens of a common type and size of the 
isolator unit over the required three cycles of test. 

3. For each specimen, there is no greater than a plus 
or minus 20% change in the initial effective stiff- 
ness of each test specimen over the 15S D [/Sd$Bd, 
but not less than 10, cycles of test specified in Item 
3 of Section 9.13.9.2.3. 

4. For each specimen, there is no greater than a 20% 
decrease in the initial effective damping over for 
the ISSdi/SdsBd, Dut not * ess tnan 10, cycles of 
test specified in Section 9.13.9.2.3. 

5. All specimens of vertical load-carrying elements 
of the isolation system remain stable up to the 
total maximum displacement for static load as 
prescribed in Section 9.13.9.2.6 and shall have a 
positive incremental force-carrying capacity. 

9.13.9.5 Design Properties of the Isolation System. 

9.13.9.5.1 Maximum and Minimum Effective 

Stiffness. At the design displacement, the maximum 



Minimum Design Loads for Buildings and Other Structures 



185 



and minimum effectiveness stiffness of the isolated 
system, k Dmax and k Dmin , shall be based on the cyclic 
tests of Item 2 of Section 9.13.9.2.3 and calculated 
by the equations: 



Z^" 



D \max 



+ Z\F. 



D \max 



^Drnax — 



2D r 



v Dmin 



(Eq. 9,13,9.5.1-1) 

/ J \Fd \min + 2^, \^ D \ min 

~ 2Do 

(Eq, 9,13,9.5,1-2) 
At the maximum displacement, the maximum and 
minimum effective stiffness of the isolation system, 
kMmax and kMmin, shall be based on the cyclic tests 
of Item 3 of Section 9.13.9.2.3 and calculated by 
the equations: 



/ , \F M \ma. 



, + Ei^ 



M \max 



^Mmax 



^Mtnin 



2D 



M 



(Eq. 9.13.9.5.1-3) 



Ei^u. + E^ 



Mimin 



2D, 



(Eq. 9.13.9.5.1-4) 
The maximum effective stiffness of the isolation sys- 
tem, k DmQX (or k Mmax ), shall be based on forces from 
the cycle of prototype testing at a test displacement 
equal to D D (or D M ) that produces the largest value 
of effective stiffness. Minimum effective stiffness of 
the isolation system, k Dmin (or k Mm in)^ sna H De based 
on forces from the cycle of prototype testing at a test 
displacement equal to D D (or Dm) that produces the 
smallest value of effective stiffness. 

For isolator units that are found by the tests 
of Sections 9.13.9.3, 9.13.9.4, and 9.13.9.5 to have 
force-deflection characteristics that vary with vertical 
load, rate of loading, or bilateral load, respectively, 
the values of kDmax and k-Mmax shall be increased and 
the values of komin an d kMmin sna ll be decreased, as 
necessary, to bound the effects of measured variation 
in effective stiffness. 

9.13.9.5.2 Effective Damping. At the design dis- 
placement, the effective damping of the isolation sys- 
tem, ftp, shall be based on the cyclic tests of Item 2 
of Section 9.13.9.3 and calculated by the equation: 



Pd 



1nkomaxD\ 



(Eq. 9.13.9.5.2-1) 



In Eq. 9.13.9.5.2-1, the total energy dissipated per 
cycle of design displacement response, T>Ed, shall be 
taken as the sum of the energy dissipated per cycle in 



all isolator units measured at a test displacement equal 
to D D . The total energy dissipated per cycle of design 
displacement response, ££/>, shall be based on forces 
and deflections from the cycle of prototype testing 
at test displacement D D that produces the smallest 
values of effective damping. 

At the maximum displacement, the effective damp- 
ing of the isolation system, /5m, shall be based on the 
cyclic tests of Item 2 of Section 9.13.9.3 and calcu- 
lated by the equation: 



Pm = 



J2 Em 



2 



27TkMmaxF>M 



(Eq. 9.13.9.5.2-2) 



In Eq. 9.13.9.5.2-2, the total energy dissipated per 
cycle of design displacement response, T,E M , shall 
be taken as the sum of the energy dissipated per cycle 
in all isolator units measured at a test displacement 
equal to D^. The total energy dissipated per cycle 
of maximum displacement response, T,Em, shall 
be based on forces and deflections from the cycle 
of prototype testing at test displacement Dm that 
produces the smallest value of effective damping. 

SECTION 9.14 
NONBUILDING STRUCTURES 

9.14.1 General. 

9.14.1.1 Nonbuilding Structures. Includes all self- 
supporting structures that carry gravity loads and that 
may be required to resist the effects of earthquake, 
with the exception of: buildings, vehicular and rail- 
road bridges, nuclear power generation plants, off- 
shore platforms, dams, and other structures excluded 
in Section 9.1.2.1. Nonbuilding structures supported by 
the earth or supported by other structures shall be 
designed and detailed to resist the minimum lateral 
forces specified in this section. Design shall conform to 
the applicable provisions of other sections as modified 
by this section. 

9.14.1.2 Design. The design of nonbuilding structures 
shall provide sufficient stiffness, strength, and ductility 
consistent with the requirements specified herein for 
buildings to resist the effects of seismic ground motions 
as represented by these design forces: 

a. Applicable strength and other design criteria shall 
be obtained from other portions of Section 9 or its 
referenced codes and standards. 

b. When applicable strength and other design cri- 
teria are not contained in or referenced by 
Section 9, such criteria shall be obtained from 
approved national standards. Where approved 
national standards define acceptance criteria in 



186 



ASCE 7-02 



terms of allowable stresses as opposed to strength, 
the design seismic forces shall be obtained from 
this Section and used in combination with other 
loads as specified in Section 2.4 of this Standard 
and used directly with allowable stresses speci- 
fied in the national standards. Detailing shall be in 
accordance with the approved national standards. 

9.14.2 Reference Standards. 

9.14.2.1 Consensus Standards. The following refer- 
ences are consensus standards and are to be consid- 
ered part of the requirements of Section 9 to the extent 
referred to in Section 9.14: 



Reference 9.14-1 



Reference 9.14-2 



Reference 9.14-3 



Reference 9.14-4 



Reference 9.14-5 



Reference 9.14-6 



Reference 9.14-7 



Reference 9.14-8 



Reference 9.14-9 



Reference 9.14-10 



ACL (1995). "Standard Practice for 
the Design and Construction of 
Cast-In-Place Reinforced Concrete 
Chimneys." ACI 307. 
ACL (1997). "Standard Practice for 
the Design and Construction of 
Concrete Silos and Stacking Tubes 
for Storing Granular Materials." 
ACI 31 3. 

ACL (2001). "Standard Practice 
for the Seismic Design of Liquid- 
Containing Concrete Structures." 
ACI 3 50 J/3 50 JR. 
ACI. (1998). "Guide to the Anal- 
ysis, Design, and Construction of 
Concrete-Pedestal Water Towers." 
ACI 371 R. 

ANSI. "Safety Requirements for 
the Storage and Handling of Anhy- 
drous Ammonia." ANSI K61.L 
American Petroleum Institute (API). 
(December 1998). "Design and 
Construction of Large, Welded, 
Low Pressure Storage Tanks." API 
620, 9th Edition, Addendum 3. 
API. (March 2000). "Welded Steel 
Tanks For Oil Storage." API 650, 
10th Edition, Addendum 1. 
API. (December 1999). "Tank 
Inspection, Repair, Alteration, and 
Reconstruction." ANSI/API 653, 
2nd Edition, Addendum 4. 
API. (May 1995). "Design and 
Construction of Liquefied Petro- 
leum Gas Installation." ANSI/API 
2510, 7th Edition. 
API. (February 1995). "Bolted 
Tanks for Storage of Production 
Liquids." Specification 12B, 14th 
Edition. 



Reference 9.14-11 

Reference 9.14-12 
Reference 9.14-13 

Reference 9.14-14 

Reference 9.14-15 

Reference 9.14-16 
Reference 9.14-17 

Reference 9.14-18 

Reference 9.14-19 

Reference 9.14-20 
Reference 9.14-21 

Reference 9,14-22 
Reference 9.13-30 



ASME. (2000). "Boiler and Pres- 
sure Vessel Code." Including 
Addenda through 2000. 
ASME. (1992). "Steel Stacks." 
ASMESTS-L 

ASME. (1995). "Gas Transmission 
and Distribution Piping Systems." 
ASMEB31.8. 

ASME. (1999). "Welded Alumi- 
num-Alloy Storage Tanks." ASME 
B96.L 

American Water Works Associa- 
tion (AWWA). (1997). "Welded 
Steel Tanks for Water Storage." 
ANSI/AWWA D100. 
AWWA. (1997). "Factory-Coated 
Bolted Steel Tanks for Water Stor- 
age." ANSI/AWWA D103. 
AWWA. (1995). "Wire- and Strand- 
Wound Circular for Prestressed 
Concrete Water Tanks." ANSI/ 
AWWA DUO, 

AWWA. (1995). "Circular Prest- 
ressed Concrete Tanks with Cir- 
cumferential Tendons." ANSI/ 
AWWA D115. 

National Fire Protection Associa- 
tion (NFPA). (2000). "Flammable 
and Combustible Liquids Code." 
ANSI/NFPA 30. 

NFPA. (2001). "Storage and Han- 
dling of Liquefied Petroleum Gas." 
ANSI/NFPA 58. 

NFPA. (2001). "Storage and Han- 
dling of Liquefied Petroleum Gases 
at Utility Gas Plants." ANSI/ 
NFPA 59. 

NFPA. (2001). "Production, Stor- 
age, and Handling of Liquefied Nat- 
ural Gas (LNG)." ANSI/NFPA 59A. 
NFPA. (2001). "Standard for Bulk 
Oxygen Systems at Consumer 
Sites." ANSI/NFPA 50. 



9.14.2.2 Accepted Standards. The following refer- 
ences are standards developed within the industry and 
represent acceptable procedures for design and construc- 
tion: 



Reference 9.14-23 



Reference 9.14-24 



ASTM. (1992). "Standard Practice 
for the Design and Manufacture of 
Amusement Rides and Devices." 
ASTM Fl 159. 

ASTM. (1998). "Standard Guide 
for Design and Construction of 
Brick Liners for Industrial Chim- 
neys." ASTM CI 298 



Minimum Design Loads for Buildings and Other Structures 



187 



Reference 9.14-25 



Reference 9.14-26 



Reference 9.14-27 



Reference 9.14-28 



Reference 9.14-29 



Reference 9.14-31 



Rack Manufacturers Institute 
(RMI). (1997). "Specification for 
the Design, Testing, and Utilization 
of Industrial Steel Storage Racks." 
U.S. Department of Transportation 
(DOT). "Pipeline Safety Regula- 
tions." Title 49CFR Part 193. 
U.S. Naval Facilities Command 
(NAVFAC). "The Seismic Design 
of Waterfront Retaining Struc- 
tures." NAVFAC R-939. 
U.S. Naval Facilities Engineering 
Command. "Piers and Wharves." 
NAVFAC DM-25.1 
U.S. Army Corps of Engineers 
(USACE). (1992). "Seismic Design 
for Buildings." Army TM 5-809-10/ 
NAVFAC P-355/ Air Force AFM 88- 
3, Chapter 13. 

Compressed Gas Association 
(GGA). (1999). "Guide for Flat- 
Bottomed LOX/LIN/LAR Storage 
Tank Systems." 1st Edition. 



9.14.3 Industry Design Standards and Recommended 
Practice. Table 9.14.3 is a cross-reference of consensus 
standards/accepted standards and the applicable nonbuild- 
ing structures. 

9.14.4 Nonbnilding Structures Supported by Other 
Structures. If a nonbuilding structure is supported above 
the base by another structure and the weight of the non- 
building structure is less than 25% of the combined weight 
of the nonbuilding structure and the supporting struc- 
ture, the design seismic forces of the supported nonbuild- 
ing structure shall be determined in accordance with the 
requirements of Section 9.6.1.3. 

If the weight of a nonbuilding structure is 25% or 
more of the combined weight of the nonbuilding structure 
and the supporting structure, the design seismic forces 
of the nonbuilding structure shall be determined based 
on the combined nonbuilding structure and supporting 
structural system. For supported nonbuilding structures 
that have nonrigid component dynamic characteristics, the 
combined system R factor shall be a maximum of 3. For 
supported nonbuilding structures that have rigid component 
dynamic characteristics (as defined in Section 9.14.5.2), 
the combined system R factor shall be the value of the 
supporting structural system. The supported nonbuilding 
structure and attachments shall be designed for the forces 
determined for the nonbuilding structure in a combined 
systems analysis. 

9.14.4.1 Architectural, Mechanical, and Electrical 
Components. Architectural, mechanical, and electri- 
cal components supported by nonbuilding structures 



shall be designed in accordance with Section 9.6 of 
this Standard. 

9.14.5 Structural Design Requirements. 

9.14.5.1 Design Basis. Nonbuilding structures having 
specific seismic design criteria established in approved 
standards shall be designed using the standards as 
amended herein. In addition, nonbuilding structures shall 
be designed in compliance with Sections 9.14.6 and 
9.14.7 to resist minimum seismic lateral forces that are 
not less than the requirements of Section 9.5.5.2 with 
the following additions and exceptions: 

1. The response modification coefficient, R, shall be 
the lesser of the values given in Table 9.14.5.1.1 
or the values in Table 9.5.2.2. 

2. For nonbuilding systems that have an R value pro- 
vided in Table 9.14.5.1.1, the minimum specified 
value in Eq. 9.5.5.2.1-3 shall be replaced by: 



C s =0.US DS I 



(Eq. 9.14.5.1-1) 



and the minimum value specified in Eq. 9.5.5.2.1-4 shall 
be replaced by: 



C, = 



O.8S1/ 



R 



(Eq. 9.14.5.1-2) 



3. The overstrength factor, Q , shall be taken from 
the same table as the R factor. 

4. The importance factor, /, shall be as given in 
Table 9.14.5.1.2. 

5. The height limitations shall be as given in 
Table 9.14.5.1.1 or the values in Table 9.5.2.2 
where not specified in Table 9.14.5.1.1. 

6. The vertical distribution of the lateral seismic 
forces in nonbuilding structures covered by this 
section shall be determined: 

a. Using the requirements of Section 9.5.5,4, or 

b. Using the procedures of Section 9.5.6, or 

c. In accordance with an approved standard appli- 
cable to the specific nonbuilding structure. 

7. For nonbuilding structural systems containing liq- 
uids, gases, and granular solids supported at the 
base as defined in Section 9.14.7.3.1, the mini- 
mum seismic design force shall not be less than 
that required by the approved standard for the spe- 
cific system. 

8. Irregular structures per Section 9.5.2.3 at sites 
where the S DS is greater than or equal to 0.50 
and that cannot be modeled as a single mass shall 
use the procedures of Section 9.5.6. 



188 



ASCE 7-02 



TABLE 9.14.3 
STANDARDS, INDUSTRY STANDARDS, AND REFERENCES 



Application 


Reference 


Steel Storage Racks 


RMI [25] 


Piers and Wharves 


NAVFAC R-939 [27], NAVFAC DM-25.1 [28] 


Welded Steel Tanks for Water Storage 


ACI 371R [4], ANSI/AWWA D100 [15], Army TM 
5-809-10/ NAVFAC P-355/ Air Force AFM 88-3 
Chapter 13 [29] 


Welded Steel and Aluminum Tanks for Petroleum 
and Petrochemical Storage 


API 620, 9th Edition, Addendum 3 [6], API 650, 10th 
Edition, Addendum 1 [7], ANSI/API 653, 2nd Edition, 
Addendum 4 [8], ASME B96.1 [14], Army TM 
5-809-10/ NAVFAC P-355/ Air Force AFM 88-3 
Chapter 13 [29] 


Bolted Steel Tanks for Water Storage 


ANSI/AWWA D 103 [16], Army TM 5-809-10/ 
NAVFAC P-355/ Air Force AFM 88-3 Chapter 13 [29] 


Bolted Steel Tanks for Petroleum and 
Petrochemical Storage 


API Specification 12B, 14th Edition [10], Army TM 
5-809-10/ NAVFAC P-355/ Air Force AFM 88-3 
Chapter 13 [29] 


Concrete Tanks for Water Storage 


ACI 350.3/350.3R [3], ANSI/AWWA DUO [17], 
ANSI/AWWA D115 [18], Army TM 5-809-10/ 
NAVFAC P-355/ Air Force AFM 88-3 Chapter 13 [29] 


Pressure Vessels 


ASME [11] 



Refrigerated Liquids Storage: 




Liquid Oxygen, Nitrogen, and Argon 


ANSI/NFPA 50 [30], GGA [31] 


Liquefied Natural Gas (LNG) 


ANSI/NFPA 59A [22], DOT Title 49CFR Part 193 [26] 


LPG (Propane, Butane, etc.) 


ANSI/API 2510, 7th Edition [9], ANSI/NFPA 30 [19], 

ANSI/NFPA 58 [20], ANSI/NFPA 59 [21] 


Ammonia 


ANSI K61.1 [5] 


Concrete Silos and Stacking Tubes 


ACI 313 [2] 


Impoundment Dikes and Walls: 




Hazardous Materials 


ANSI K6 1.1 [5] 


Flammable Materials 


ANSI/NFPA 30 [19] 


Liquefied Natural Gas 


ANSI/NFPA 59A [22], DOT Title 49CFR Part 193 [26] 


Gas Transmission and Distribution Piping Systems 


ASME B3 1.8 [13] 


Cast-in-Place Concrete Stacks and Chimneys 


ACI 307 [1] 


Steel Stacks and Chimneys 


ASME STS-1 [12] 


Guyed Steel Stacks and Chimneys 


ASMESTS-1 [12] 


Brick Masonry Liners for Stacks and Chimneys 


ASTM CI 298 [24] 


Amusement Structures 


ASTMF1159 [23] 



Minimum Design Loads for Buildings and Other Structures 



189 



TABLE 9.14.5.1.1 
SEISMIC COEFFICIENTS FOR NONBUILDING STRUCTURES 



Nonbuilding Structure Type 


R 


S2 


c d 


Structural System 
and Height 
Limits (ft) b 


Seismic Design Category 


A&B 


c 


D 


E&F 


Nonbuilding frame systems: 

Concentric braced frames of steel 
Special concentric braced frames of steel 


See Table 9.5.2.2 


NL 
NL 


NL 
NL 


NL 
NL 


NL 
NL 


Moment-resisting frame systems: 
Special moment frames of steel 
Ordinary moment frames of steel 
Special moment frames of concrete 
Intermediate moment frames of concrete 
Ordinary moment frames of concrete 


See Table 9.5.2.2 


NL 
NL 
NL 
NL 
NL 


NL 

NL 

NL 

NL- 

50 


NL 
50 
NL 
50 c 

NP 


NL 
50 
NL 
50 c 
NP 


Steel storage racks 


4 


2 


V- 


NL 


NL 


NL 


NL 


Elevated tanks, vessels, bins, or hoppers 3 :. 
On braced legs 
On unbraced legs 

Irregular braced legs single pedestal or skirt- supported 
Welded steel 
Concrete 


3 
3 

2 
2 
2 


2 
2 

2 
2 

2 


2 ] - 

2 ] - 

2 
2 
2 


NL 

NL 
NL 

NL 
NL 


NL 
NL 

NL 
NL 
NL 


NL 
NL 

NL 
NL 
NL 


NL 

NL 
NL 
NL 
NL 


Horizontal, saddle supported welded steel vessels 


3 


2 


2 ] - 

Z 2 


NL 


NL 


NL 


NL 


Tanks or vessels supported on structural towers similar to 
buildings 


3 


2 


2 


NL 


NL 


NL 


NL 


Flat bottom, ground supported tanks, or vessels: 
Anchored (welded or bolted steel) 
Unanchored (welded or bolted steel) 

Reinforced or prestressed concrete: 
Tanks with reinforced nonsliding base 

Tanks with anchored flexible base 


3 

2 ] - 

2 

2 
3 


2 

2 

2 
2 


2 l - 

2 

2 

2 

2 


NL 
NL 

NL 
NL 


NL 

NL 

NL 
NL 


NL 
NL 

NL 
NL 


NL 
NL 

NL 
NL 


Tanks with unanchored and unconstrained flexible base: 
Other material: 


H 
H 


H 
H 


4 


NL 

NL 


NL 
NL 


NL 
NL 


NL 
NL 


Cast-in-place concrete silos, stacks, and chimneys having walls 
continuous to the foundation 


3 


H 


3 


NL 


NL 


NL 


NL 


Ail other reinforced masonry structures not similar to buildings 


3 


2 


H 


NL 


NL 


50 


50 


All other nonreinforced masonry structures not similar to 
buildings 


U 


2 


H 


NL 


50 


50 


50 


All other steel and reinforced concrete distributed mass 
cantilever structures not covered herein including stacks, 
chimneys, silos, and skirt-supported vertical vessels that are 
not similar to buildings 


3 


2 


A 


NL 


NL 


NL 


NL 



(continued) 



190 



ASCE 7-02 



TABLE 9.14.5.1.1 - continued 
SEISMIC COEFFICIENTS FOR NONBUILDING STRUCTURES 



Nonbuilding Structure Type 


R 


«o 


c d 


Structural System 
and Height 
Limits (ft) b 


Seismic Design Category 


A&B 


c 


D 


E&F 


Trussed towers (freestanding or guyed), guyed stacks and 
chimneys 


3 


2 


A 


NL 


NL 


NL 


NL 


Cooling towers: 
Concrete or steel 

Wood frame 


3± 

J 2 


3 


3 

3 


NL 
NL 


NL 

NL 


NL 
50 


NL 
50 


Telecommunication towers 
Truss: Steel 
Pole: Steel 
Wood 
Concrete 
Frame: Steel 
Wood 
Concrete 


3 

3 
2 


ii 


3 


NL 
NL 
NL 
NL 

NL 
NL 
NL 


NL 
NL 
NL 
NL 
NL 
NL 
NL 


NL 

NL 
NL 
NL 
NL 
NL 
NL 


NL 
NL 
NL 
NL 
NL 
NL 
NL 


Amusement structures and monuments 


2 


2 


2 


NL 


NL 


NL 


NL 


Inverted pendulum-type structures (except elevated tanks, 
vessels, bins, and hoppers) 


2 


2 


2 


NL 


NL 


NL 


NL 


Signs and billboards 


H 


i! 


3 


NL 


NL 


NL 


NL 


All other self-supporting structures, tanks, or vessels not 
covered above or by approved standards that are similar to 
buildings 


H 


2 


2 ] - 


NL 


50 


50 


50 



a Support towers similar to building-type structures, including those with irregularities 

structures) shall comply with the requirements of Section 9.5.2.6. 

b Height shall be measured from the base. 

c See exception to Section 9.14.6.1. 

NL = No limit. 

NP = Not permitted. 



(see Section 9.5.2.3 of this Standard for definition of irregular 



9. Where an approved national standard provides 
a basis for the earthquake-resistant design of a 
particular type of nonbuilding structure covered 
by Section 9.14, such a standard shall not be used 
unless the following limitations are met: 

a. The seismic ground acceleration, and seismic 
coefficient, shall be in conformance with the 
requirements of Sections 9.4.1 and 9.4.1.2.5, 
respectively. 

b. The values for total lateral force and total 
base overturning moment used in design shall 
not be less than 80% of the base shear value 
and overturning moment, each adjusted for 
the effects of soil-structure interaction that is 
obtained using this Standard. 



10. The base shear is permitted to be reduced in 
accordance with Section 9.5.9.2.1 to account for 
the effects of soil-structure interaction. In no 
case shall the reduced base shear, V, be less 
than 0.7 V. 

9.14.5.1.1 Seismic Factors. 

9.14.5.1.2 Importance Factors and Seismic Use 
Group Classifications. The importance factor (I) and 
seismic use group for nonbuilding structures are 
based on the relative hazard of the contents and the 
function. The value of / shall be the largest value 
determined by the approved standards or the largest 
value as selected from Table 9.14.5.L2 or as specified 
elsewhere in Section 9.14. 



Minimum Design Loads for Buitdings and Other Structures 



191 



TABLE 9.14.5.1.2 

IMPORTANCE FACTOR (!) AND SESSIVHC USE 

GROUP CLASSIFICATION FOR 

NONBUILDING STRUCTURES 



Importance Factor 


1 = 1.0 


1 = 1.25 


1 = 1.5 


Seismic Use Group 


I 


fl 


III 


Hazard 


H-I 


H-II 


H-I1I 


Function 


F-I 


F-II 


F-III 



H-I. The nonbuilding structures that are not assigned to H-II or 
H-III. 

H-II. The nonbuilding structures containing hazardous materials 
and classified as a Category III structure in Table 1-1. 

H-III. The nonbuilding structures containing extremely hazardous 
materials and classified as a Category IV structure in 
Table 1-1. 

F-I. Nonbuilding structures not classified as F-II or F-III. 

F-II. Nonbuilding structures classified as Category III structures 
in Table 1-1. 

F-III. The nonbuilding structures classified as Category IV struc- 
tures (essential facilities) in Table 1-1. 

9.14.5.2 Rigid Nonbuilding Structures. Nonbuilding 
structures that have a fundamental period, 7\ less than 
0.06 s, including their anchorages, shall be designed for 
the lateral force obtained from the following: 



V = 0.30S DS WI 



(Eq. 9.14.5.2) 



where 



V = the total design lateral seismic base shear 
force applied to a nonbuilding structure 
S DS — the site design response acceleration as 
determined from Section 9.4.1.2.5 
W = nonbuilding structure operating weight 
/ = the importance factor as determined from 
Table 9.14.5.1.2 

The force shall be distributed with height in accordance 
with Section 9.5.5.4. 

9.14.5.3 Loads. The weight W for nonbuilding struc- 
tures shall include all dead load as defined for structures 
in Section 9.5.5.2. For purposes of calculating design 
seismic forces in nonbuilding structures, W also shall 
include all normal operating contents for items such as 
tanks, vessels, bins, hoppers, and the contents of piping. 
W shall include snow and ice loads when these loads 
constitute 25% or more of W or when required by the 
building official based on local environmental character- 
istics. 



9.14.5.5 Drift Limitations. The drift limitations of 
Section 9.5.2.8 need not apply to nonbuilding structures 
if a rational analysis indicates they can be exceeded with- 
out adversely affecting structural stability or attached or 
interconnected components and elements such as walk- 
ways and piping. P -delta effects shall be considered 
when critical to the function or stability of the structure. 

9.14.5.6 Materials Requirements. The requirements 
regarding specific materials in Sections A.9.8, A. 9. 9, and 
A.9.11 shall be applicable unless specifically exempted 
in Section 9.14. 

9.14.5.7 Deflection Limits and Structure Separation. 

Deflection limits and structure separation shall be deter- 
mined in accordance with this Standard unless specifi- 
cally amended in Section 9.14. 

9.14.5.8 Site-Specific Response Spectra. Where requi- 
red by an approved standard or the authority having 
jurisdiction, specific types of nonbuilding structures 
shall be designed for site- specific criteria that accounts 
for local seismicity and geology, expected recurrence 
intervals and magnitudes of events from known seismic 
hazards (reference section 9.4.1.3 of this Standard). If 
a longer recurrence interval is defined in the approved 
standard for the nonbuilding structure such as LNG tanks 
[Ref. 9.14-22], the recurrence interval required in the 
approved standard shall be used. 

9.14.6 Nonbuilding Structures Similar to Buildings. 

9.14.6.1 General. Nonbuilding structures that have 
structural systems that are designed and constructed in a 
manner similar to buildings and have a dynamic response 
similar to building structures shall be designed similar to 
building structures and in compliance with this Standard 
with exceptions as contained in this section. 

This general category of nonbuilding structures shall 
be designed in accordance with Sections 9.5 and 9.14.5. 

The lateral force design procedure for nonbuild- 
ing structures with structural systems similar to build- 
ing structures (those with structural systems listed in 
Table 9.5.2.2) shall be selected in accordance with the 
force and detailing requirements of Section 9.5.2.1. The 
height limitations shall be as given in Table 9.14.1.1 
or the values in Table 9.5.2.2 where not specified in 
Table 9.14.5.1.1. 



9.14.5.4 Fundamental Period. The fundamental period 
of the nonbuilding structure shall be determined by 
methods as prescribed in Section 9.5.5.3 or by other 
rational methods. 



Exception: Intermediate moment frames of rein- 
forced concrete shall not be used at sites where the 
seismic coefficient Sds is greater than or equal to 
0.50 unless 



192 



ASCE 7-02 



1. The nonbuilding structure is less than 50 ft 
(15.2 m) in height and 

2, R = 3.0 is used for design. 

The combination of load effects, E, shall be determined 
in accordance with Section 9.5.2.7. 

9.14,6.2 Pipe Racks. 



of Cs used shall not be less than the value for F p 
determined in accordance with Section 9.6.2.4.1c 
of this Standard, where R p is taken as equal to R 
from Ref. 9.14-25 and a p is taken as equal to 2.5. 

9.14.6.3.1 General Requirements. Steel storage 
racks shall satisfy the force requirements of this 
section. 



9.14.6.2.1 Design Basis. In addition to the provisions 
of 9.14.6.1, pipe racks supported at the base of 
the structure shall be designed to meet the force 
requirements of Sections 9.5.5 or 9.5.6. 

Displacements of the pipe rack and potential for 
interaction effects (pounding of the piping system) 
shall be considered using the amplified deflections 
obtained from the following formula: 



S x 



Cd&x 



(Eq. 9.14.6.2.1) 



where 



Q = deflection amplification factor in 

Table 9.14.5.1.1 
S xe = deflections determined using the prescribed 

seismic design forces of this Standard 
/ = importance factor determined from 

Table 9.14.5.1.2 

Exception: The importance factor, /, shall be 
determined from Table 9.14.5.1.2 for the calcula- 
tion of 5^. 

See Section 9.6.3.11 for the design of piping 
systems and their attachments. Friction resulting from 
gravity loads shall not be considered to provide 
resistance to seismic forces. 

9.14.6.3 Steel Storage Racks. In addition to the provi- 
sions of 9.14.6.1, steel storage racks shall be designed 
in accordance with the provisions of Sections 9.14.6.3.1 
through 9.14.6.3.4. Alternatively, steel storage racks 
shall be permitted to be designed in accordance with the 
method defined in Section 2.7 "Earthquake Forces" of 
Ref. 9.14-25, where the following changes are included: 

1. The values of C a and C v used shall equal S D s /2.5 
and S D \, respectively, where S DS and S D \ are 
determined in accordance with Section 9.4.1.2.5 of 
this Standard. 

2. The value of I p used shall be determined in 
accordance with Section 9.6.1.5 of this Standard. 

3. For storage racks located at or below grade, the 
value of Cs used shall not be less than 0.14 Sds- 
For storage racks located above grade, the value 



Exception: Steel storage racks supported at the 
base are permitted to be designed as structures 
with an R of 4, provided that the requirements of 
Section 9.5 are met. Higher values of R are per- 
mitted to be used when the detailing requirements 
of reference documents of Section 9.8 as modified 
in Section A9.8 are met. The importance factor / 
shall be taken equal to the I p values in accordance 
with Section 9.6.1.5. 

9.14.6.3.2 Operating Weight. Steel storage racks 
shall be designed for each of the following conditions 
of operating weight, W or W p . 

a. Weight of the rack plus every storage level 
loaded to 67% of its rated load capacity. 

b. Weight of the rack plus the highest storage level 
only loaded to 100% of its rated load capacity. 

The design shall consider the actual height of the 
center of mass of each storage load component. 

9.14.6.3.3 Vertical Distribution of Seismic Forces. 
For all steel storage racks, the vertical distribution of 
seismic forces shall be as specified in Section 9.5.5.4 
and in accordance with the following: 

a. The base shear, V, of the typical structure shall 
be the base shear of the steel storage rack when 
loaded in accordance with Section 9.14.6.3.2. 

b. The base of the structure shall be the floor 
supporting the steel storage rack. Each steel 
storage level of the rack shall be treated as a 
level of the structure with heights h L and h x 
measured from the base of the structure. 

c. The factor k may be taken as 1.0. 

d. The factor / shall be in accordance with 
Section 9.6.1.5. 

9.14.6.3.4 Seismic Displacements. Steel storage rack 
installations shall accommodate the seismic displace- 
ment of the storage racks and their contents relative 
to all adjacent or attached components and elements. 
The assumed total relative displacement for storage 
racks shall be not less than 5% of the height above 



Minimum Design Loads for Buildings and Other Structures 



193 



the base unless a smaller value is justified by test data 
or analysis in accordance with Section 9.1.2.5. 

9.14.6.4 Electrical Power Generating Facilities. 

9.14.6.4.1 General. Electrical power generating facil- 
ities are power plants that generate electricity by 
steam turbines, combustion turbines, diesel genera- 
tors, or similar turbo machinery. 

9.14.6.4.2 Design Basis. In addition to the provisions 
of 9.14.6.1, electrical power generating facilities shall 
be designed using this Standard and the appropriate 
factors contained in Section 9.14.5. 

9.14.6.5 Structural Towers for Tanks and Vessels. 

9.14.6.5.1 General. In addition to the provisions of 
9.14.6.1, structural towers which support tanks and 
vessels shall be designed to meet the provisions 
of Section 9.14.4 In addition, the following special 
considerations shall be included: 

a. The distribution of the lateral base shear from 
the tank or vessel onto the supporting structure 
shall consider the relative stiffness of the tank 
and resisting structural elements. 

b. The distribution of the vertical reactions from 
the tank or vessel onto the supporting structure 
shall consider the relative stiffness of the tank 
and resisting structural elements. When the tank 
or vessel is supported on grillage beams, the 
calculated vertical reaction due to weight and 
overturning shall be increased at least 20% to 
account for nonuniform support. The grillage 
beam and vessel attachment shall be designed 
for this increased design value. 

c. Seismic displacements of the tank and ves- 
sel shall consider the deformation of the sup- 
port structure when determining P -delta effects 
or evaluating required clearances to prevent 
pounding of the tank on the structure. 

9.14.6.6 Piers and Wharves. 

9.14.6.6.1 General. Piers and wharves are structures 
located in waterfront areas that project into a body of 
water or parallel the shoreline. 



displaced water. The additional seismic mass equal 
to the mass of the displaced water shall be included 
as a lumped mass on the submerged element, and 
shall be added to the calculated seismic forces of the 
pier or wharf structure. Seismic dynamic forces from 
the soil shall be determined by the registered design 
professional. 

The design shall account for the effects of lique- 
faction on piers and wharves as required. 

9.14.7 Nonbuilding Structures Not Similar to 
Buildings. 

9.14.7.1 General. Nonbuilding structures that have 
structural systems that are designed and constructed in 
a manner such that the dynamic response is not similar 
to buildings shall be designed in compliance with this 
Standard with exceptions as contained in this section. 

This general category of nonbuilding structures shall 
be designed in accordance with this Standard and the 
specific applicable approved standards. Loads and load 
distributions shall not be less than those determined in 
this Standard. 

The combination of load effects, £, shall be deter- 
mined in accordance with Section 9.5.2.7. 

Exception: The redundancy/reliability factor, p, per 
Section. 9.5.2.4 shall be taken as 1. 

9.14.7.2 Earth-Retaining Structures. 

9.14.7.2.1 General. This section applies to all earth- 
retaining walls. The applied seismic forces shall be 
determined in accordance with Section 9.7.5.1 with a 
geotechnical analysis prepared by a registered design 
professional. 

The seismic use group shall be determined by 
the proximity of the retaining wall to buildings and 
other structures. If failure of the retaining wall would 
affect an adjacent structure, the Seismic Use Group 
shall not be less than that of the adjacent structure, 
as determined in Section 9.1.3. Earth-retaining walls 
are permitted to be designed for seismic loads as 
either yielding or nonyielding walls. Cantilevered 
reinforced concrete retaining walls shall be assumed 
to be yielding walls and shall be designed as simple 
flexural wall elements. 

9.14.7.3 Tanks and Vessels. 



9.14.6.6.2 Design Basis. In addition to the provisions 
of 9.14.6.1, piers and wharves shall be designed to 
comply with this Standard and approved standards. 
Seismic forces on elements below the water level 
shall include the inertial force of the mass of the 



9.14.73.1 General. This section applies to all tanks, 
vessels, bins and silos, and similar containers storing 
liquids, gases, and granular solids supported at the 
base (hereafter referred to generically as tanks and 
vessels). Tanks and vessels covered herein include 



194 



ASCE 7-02 



reinforced concrete, pres tressed concrete, steel, alu- 
minum, and fiber-reinforced plastic materials. Tanks 
supported on elevated levels in buildings shall be 
designed in accordance with Section 9.6.3.9. 

9.14.73.2 Design Basis. Tanks and vessels storing 
liquids, gases, and granular solids shall be designed in 
accordance with this Standard and shall be designed 
to meet the requirements of the applicable approved 
standards shown in Table 9.14.3 and Section 9 of this 
Standard as defined in this section. Resistance to seis- 
mic forces shall be determined from a substantiated 
analysis based on the approved standards shown in 
Table 9.14.3. 

a. Damping for the convective (sloshing) force 
component shall be taken as 0.5%. 

b. Impulsive and convective components shall be 
combined by the direct sum or the square root 
of the sum of the squares (SRSS) method 
when the modal periods are separated. If sig- 
nificant modal coupling may occur, the com- 
plete quadratic combination (CQC) method 
shall be used. 

c. Vertical earthquake forces shall be considered 
in accordance with the appropriate approved 
national standard. If the approved national 
standard permits the user the option of includ- 
ing or excluding the vertical earthquake force, 
to comply with this Standard, it shall be 
included. For tanks and vessels not covered 
by an approved national standard, the vertical 
earthquake force shall be defined as 67% of the 
equivalent lateral force. 

9.14.7.3.3 Strength and Ductility. Structural com- 
ponents and members that are part of the lat- 
eral support system shall be designed to provide 
the following: 

a. Connections and attachments for anchorage and 
other lateral force-resisting components shall be 
designed to develop the strength of the anchor 
(e.g., minimum published yield strength, F y in 
direct tension, plastic bending moment), or Q 
times the calculated element design force. 

b. Penetrations, manholes, and openings in shell 
components shall be designed to maintain the 
strength and stability of the shell to carry tensile 
and compressive membrane shell forces. 

c. Support towers for tanks and vessels with 
irregular bracing, unbraced panels, asymmet- 
ric bracing, or concentrated masses shall be 
designed using the provisions of Section 9.5.2.3 



for irregular structures. Support towers using 
chevron or eccentric braced framing shall com- 
ply with the requirements of Section 9.5. Sup- 
port towers using tension only bracing shall 
be designed such that the full cross-section 
of the tension element can yield during over- 
load conditions. 

d. In support towers for tanks and vessels, com- 
pression struts that resist the reaction forces 
from tension braces shall be designed to resist 
the lesser of the yield load of the brace (A g F y ), 
or Q times the calculated tension load in 
the brace. 

e. The vessel stiffness relative to the support 
system (foundation, support tower, skirt, etc.) 
shall be considered in determining forces in 
the vessel, the resisting components, and the 
connections. 

f. For concrete liquid-containing structures, sys- 
tem ductility and energy dissipation under 
unfactored loads shall not be allowed to be 
achieved by inelastic deformations to such 
a degree as to jeopardize the serviceabil- 
ity of the structure. Stiffness degradation and 
energy dissipation shall be allowed to be 
obtained either through limited microcracking 
or by means of lateral force-resistance mecha- 
nisms that dissipate energy without damaging 
the structure. 



9.14.7.3.4 Flexibility of Piping Attachments. Pip- 
ing systems connected to tanks and vessels shall 
consider the potential movement of the connection 
points during earthquakes and provide sufficient flex- 
ibility to avoid release of the product by failure of 
the piping system. Forces and deformations imparted 
by piping systems or other attachments shall not 
exceed the design limitations at points of attach- 
ment to the tank or vessel shell. Mechanical devices 
which add flexibility such as bellows, expansion 
joints, and other flexible apparatus may be used when 
they are designed for seismic loads and displace- 
ments. 

Unless otherwise calculated, the minimum dis- 
placements in Table 9.14.7.3.4 shall be assumed. 
For attachment points located above the support 
or foundation elevation, the displacements in Table 
9.14.7.3.4 shall be increased to account for drift of 
the tank or vessel relative to the base of support. 

When the elastic deformations are calculated, the 
minimum design displacements for piping attach- 
ments shall be the calculated displacements at the 
point of attachment increased by the amplification 
factor Cd- 



Minimum Design Loads for Buildings and Other Structures 



195 



TABLE 9.14.7.3.4 
MINIMUM DISPLACEMENTS FOR PIPING ATTACHMENTS 



Anchored Tanks or Vessels 


Displacements 
(in.) 


Vertical displacement relative to support or foundation 


2 


Horizontal (radial and tangential) relative to support or foundation 


0.5 


Unanchored Tanks or Vessels (at grade) 




Vertical displacement relative to support or foundation 

If designed to meet approved standard 

If designed for seismic loads per these provisions but not covered by an 
approved standard 

For tanks and vessels with a diameter <40 ft, horizontal (radial and tangential) 
relative to support or foundation 


6 
12 

8 



The values given in Table 9.14.73.4 do not include 
the influence of relative movements of the foundation 
and piping anchorage points due to foundation move- 
ments (e.g., settlement, seismic displacements). The 
effects of the foundation movements shall be included 
in the piping system design including the determina- 
tion of the mechanical loading on the tank or vessel 
and the total displacement capacity of the mechanical 
devices intended to add flexibility. 

9.14.7.3,5 Anchorage. Tanks and vessels at grade 
shall be permitted to be designed without anchor- 
age when they meet the requirements for unan- 
chored tanks in approved standards. Tanks and ves- 
sels supported above grade on structural towers or 
building structures shall be anchored to the support- 
ing structure. 

The following special detailing requirements shall 
apply to steel tank anchor bolts in seismic regions 
where Sds > 0.5, or where the structure is classified 
as Seismic Use Group III. 

a. Hooked anchor bolts (L- or J-shaped embedded 
bolts) or other anchorage systems based solely 
on bond or mechanical friction shall not be used 
when Sds > 0.33. Postinstalled anchors may be 
used provided that testing validates their ability 
to develop yield load in the anchor under cyclic 
loads in cracked concrete. 

b. When anchorage is required, the anchor embed- 
ment into the foundation shall be designed to 
develop the minimum specified yield strength 
of the anchor. 

9.14.73.6 Ground-Supported Storage Tanks for 
Liquids. 

9.14.7.3.6.1 General. Ground-supported, flat bot- 
tom tanks storing liquids shall be designed to resist 



the seismic forces calculated using one of the fol- 
lowing procedures: 

a. The base shear and overturning moment 
calculated as if tank and the entire contents 
are a rigid mass system per Section 9.14.5.2 
of this Standard, or 

b. Tanks or vessels storing liquids in Seis- 
mic Use Group III, or with a diameter 
greater than 20 ft shall be designed to con- 
sider the hydrodynamic pressures of the liq- 
uid in determining the equivalent lateral 
forces and lateral force distribution per the 
approved standards listed in Table 9.14.3 
and the requirements of Section 9.14.7.3 of 
this Standard. 

c. The force and displacement provisions of 
Section 9.14.5 of this Standard. 

The design of tanks storing liquids shall con- 
sider the impulsive and convective (sloshing) 
effects and their consequences on the tank, founda- 
tion, and attached elements. The impulsive compo- 
nent corresponds to the high-frequency amplified 
response to the lateral ground motion of the tank 
roof, shell, and portion of the contents that moves 
in unison with the shell. The convective compo- 
nent corresponds to the low-frequency amplified 
response of the contents in the fundamental slosh- 
ing mode. Damping for the convective component 
shall be 0.5% for the sloshing liquid unless oth- 
erwise defined by the approved national standard. 
The following definitions shall apply: 

T c — natural period of the first (convective) 

mode of sloshing 
Tt — fundamental period of the tank structure 

and impulsive component of the content 



196 



ASCE 7-02 



Vj — base shear due to impulsive component 
from weight of tank and contents 

V c — base shear due to the convective compo- 
nent of the effective sloshing mass 

The seismic base shear is the combination of 
the impulsive and convective components: 



v - v- + v c 



where 






SgilWj 

R 

s ac iw c 

R 



(Eq. 9.14.7.3.6.1-1) 

(Eq. 9.14.7.3.6.1-2) 
(Eq. 9.14.7.3.6.1-3) 



S ai = the spectral acceleration as a multiplier of 
gravity including the site impulsive components at 
period 7} and 5% damping 
For Tj < T s 



(Eq. 9.14.7.3.6.1-4) 





S ■ — 


Sds 


For T t 


>T S 






b a i == 





(Eq. 9.14.73.6.1-5) 



Notes: 



a. When an approved national standard is used 
in which the spectral acceleration for the tank 
shell, and the impulsive component of the 
liquid is independent of 7}, then S ai ~ Sos- 

b. Eq. 9.147.3.6.1-5 shall not be less than 
0.14 S D $ R and in addition in Seismic 
Design Categories E and F shall not be taken 
less than 0.8 S\. 

S ac — the spectral acceleration of the slosh- 
ing liquid based on the sloshing period T c and 
0.5% damping 

For T c < 4.0 sec 



For T c > 4.0 sec 
6Sdi 



bar — 



T} 



(Eq. 9.14.73.6.1-6) 



(Eq. 9.14.73.6.1-7) 



where 



T = 2tt 



\ 



D 



3.68gtanh 



3.68# 
D 



(Eq. 9.14.73.6.1-8) 
Minimum Design Loads for Buildings and Other Structures 



and 
where 

D = the tank diameter in ft (or meters), H — 
liquid height in ft (or meters), and 
g = acceleration due to gravity in 
consistent units 

W/ = impulsive weight (impulsive component of 
liquid, roof and equipment, shell, bottom, 
and internal components) 

W c = the portion of the liquid weight sloshing 

The general design response spectra for ground- 
supported liquid storage tanks is shown in 
Figure 9.14.7.3.6-1. 

9.14.73.6.1.1 Distribution of Hydrodynamic 
and Inertia Forces. Unless otherwise required 
by the appropriate approved standard in Table 
9.14.3, the method given in Ref. 9.14-3 may 
be used to determine the vertical and horizon- 
tal distribution of the hydrodynamic and inertia 
forces on the walls of circular and rectangu- 
lar tanks. 

9.14.73.6.1.2 Freeboard. Sloshing of the liq- 
uid within the tank or vessel shall be considered 
in determining the freeboard required above the 
top capacity liquid level. A minimum freeboard 
(S s ) shall be provided per Table 9.14.7.3.6.1.2. 
The height of the sloshing wave is permitted to 
be calculated as: 



8.=0.5DIS a 



(Eq. 9.14.73.6.1.2) 



9.14.73.6.13 Equipment and Attached Pip- 
ing. Equipment, piping and walkways or other 




Period, T (sec) 

FIGURE 9.14.7.3.6-1 

DESIGN RESPONSE SPECTRA FOR GROUND-SUPPORTED 

LIQUBD STORAGE TANKS 



197 



TABLE 9.14.7.3.6.1.2 
MINIMUM REQUIRED FREEBOARD 



Value of S DS 


Seismic Use Group 


1 


II 


Hi 


S DS <0A67 g 


a 


a 


5, c 


0.167 g<S^<0.33 g 


a 


a 


5/ 


0.33 g < S DS < 0.50 g 


a 


0JS s b 


£, c 


S DS > 0.50 g 


a 


0.7<5, b 


$s C 



a No minimum freeboard is required. 

b A freeboard equal to 0.7 S s is required unless one of the following 

alternatives is provided: 

1. Secondary containment is provided to control the product spill. 

2. The roof and supporting structure are designed to contain the 
sloshing liquid. 

c Freeboard equal to the calculated wave height, 8 S , is required unless one 
of the following alternatives is provided: 

1 . Secondary containment is provided to control the product spill. 

2. The roof and supporting structure are designed to contain the 
sloshing liquid. 



appurtenances attached to the structure shall 
be designed to accommodate the displacements 
imposed by seismic forces. For piping attach- 
ments, see Section 9.14.7.3.4. 

9.14.73.6.1.4 Internal Components. The at- 
tachments of internal equipment and accessories 
which are attached to the primary liquid or 
pressure-retaining shell or bottom, or provide 
structural support for major components (e.g., 
a column supporting the roof rafters), shall be 
designed for the lateral loads due to the sloshing 
liquid in addition to the inertial forces by a 
substantiated analysis method. 

9.14.7.3.6.1.5 Sliding Resistance. The transfer 
of the total lateral shear force between the tank 
or vessel and the subgrade shall be considered: 

a. For unanchored flat bottom steel tanks, 
the overall horizontal seismic shear force 
is permitted to be resisted by friction 
between the tank bottom and the foun- 
dation or subgrade. Unanchored storage 
tanks shall be designed such that sliding 
will not occur when the tank is full of 
stored product. The maximum calculated 
seismic base shear, V, shall not exceed: 



V < Wtan 30 



(Eq. 9.14.7.3.6.1.5) 



W shall be determined using the effec- 
tive weight of the tank, roof, and con- 
tents after reduction for coincident verti- 
cal earthquake. Lower values of the fric- 
tion factor shall be used if the design of 
the tank bottom to supporting foundation 
does not justify the friction value above 
(e.g., leak detection membrane beneath 
the bottom with a lower friction factor, 
smooth bottoms, etc.). Alternatively, the 
friction factor shall be permitted to be 
determined by testing in accordance with 
Section 9.1.2.5. 

b. No additional lateral anchorage is required 
for anchored steel tanks designed in accor- 
dance with approved standards. 

c. The lateral shear transfer behavior for 
special tank configurations (e.g., shovel 
bottoms, highly crowned tank bottoms, 
tanks on grillage) can be unique and are 
beyond the scope of these provisions. 

9.14.7.3.6.1.6 Local Shear Transfer. Local 
transfer of the shear from the roof to the wall 
and the wall, of the tank into the base shall be 
considered. For cylindrical tanks and vessels, 
the peak local tangential shear per unit length 
shall be calculated by: 

v m ax = — (Eq. 9.14.7.3.6.1.6) 

jxD 

a. Tangential shear in flat bottom steel tanks 
shall be transferred through the welded 
connection to the steel bottom. This 
transfer mechanism is deemed acceptable 
for steel tanks designed in accordance 
with the approved standards where $os < 
1.0 g. 

b. For concrete tanks with a sliding base 
where the lateral shear is resisted by 
friction between the tank wall and the 
base, the friction coefficient value used for 
design shall not exceed tan 30 degrees. 

c. Fixed-base or hinged-base concrete tanks, 
transfer the horizontal seismic base shear 
shared by membrane (tangential) shear 
and radial shear into the foundation. For 
anchored flexible-base concrete tanks, the 
majority of the base shear is resisted 
by membrane (tangential) shear through 
the anchoring system with only insignif- 
icant vertical bending in the wall. The 
connection between the wall and floor 



198 



ASCE 7-02 



shall be designed to resist the maximum 
tangential shear. 

9.14.7.3.6.1.7 Pressure Stability. For steel 
tanks, the internal pressure from the stored 
product stiffens thin cylindrical shell structural 
elements subjected to membrane compression 
forces. This stiffening effect may be considered 
in resisting seismically induced compressive 
forces if permitted by the approved standard or 
the authority having jurisdiction. 

9.14.7.3.6.1.8 Shell Support. Steel tanks rest- 
ing on concrete ring walls or slabs shall have 
a uniformly supported annulus under the shell. 
Uniform support shall be provided by one of 
the following methods: 

a. Shimming and grouting the annulus. 

b. Using fiberboard or other suitable padding. 

c. Using butt-welded bottom or annular plates 
resting directly on the foundation. 

d. Using closely spaced shims (without struc- 
tural grout) provided that the localized 
bearing loads are considered in the tank 
wall and foundation to prevent local crip- 
pling and spalling. 

Anchored tanks shall be shimmed and grouted. 
Local buckling of the steel shell for the peak 
compressive force due to operating loads and 
seismic overturning shall be considered. 

9.14.7.3.6.1.9 Repair, Alteration, or Recon- 
struction. Repairs, modifications, or reconstruc- 
tion (i.e., cut down and re-erect) of a tank 
or vessel shall conform to industry standard 
practice and this Standard. For welded steel 
tanks storing liquids, see Ref. 9.14-8 and the 
approved national standard in Table 9.14.3. 
Tanks that are relocated shall be re-evaluated 
for the seismic loads for the new site and the 
requirements of new construction in accordance 
with the appropriate approved national standard 
and this Standard. 

9.14.7.3.7 Water and Water Treatment Tanks and 
Vessels. 

9.14.7.3.7.1 Welded Steel. Welded steel water 
storage tanks and vessels shall be designed in accor- 
dance with the seismic requirements of Ref. 9.14- 
15 except that the design input forces shall be mod- 
ified as follows: 



The equations for base shear and overturning 
moment are defined by the following equations for 
allowable stress design procedures: 

For T s < T c < 4.0 sec 



y ACT = 



SpsI 
(1.4/?) 



(W s + W r + W f + Wi) 



+ 1.5 — W 2 



M = 



SnsI 



(1.4*) 



(Eq. 9.14.7.3.7.1-1) 

(WsXs + WrHt + WiXi) 



1.5 — W 2 X 2 

* c 



(Eq. 9.14.7.3.7.1-2) 



For T c > 4.0 sec 
SdsI 



Vact = 



(1.4/?) 



(W, + W r + Wf + W { ) 



T 

■6~W 2 



M = 



SdsI 
(1.4/?) L 



(Eq. 9.14.7.3.7.1-3) 

(WsXs + WrHt + WtXi) 



+ 6^W 2 X 2 



(Eq. 9.14.7.3.7.1-4) 

a. Substitute the above equations for Eqs. 13-4 
and 13-8 of Ref. 9.14-15 where S DS and 
Ts are defined in Section 9.4.1.2.5 and R is 
defined in Table 9.14.5.1.1. 

b. The hydrodynamic seismic hoop tensile 
stress is defined in Eqs. 13-20 through 13-25 
in Ref. 9.14-15. When using these equations, 

2/ 

substitute Eq. 9.14.7.3.7.1-5 for — - directly 

Rw 

into the equations. 



S DS I 
2.5(1.4/?) 



(Eq. 9.14.7.3.7.1-5) 



c. Sloshing height shall be calculated per 
Section 9.14.7.3.7.1.2 instead of Eq. 13-26 
of Ref. 9.14-15. 

9.14.7.3.7.2 Bolted Steel. Bolted steel water stor- 
age structures shall be designed in accordance with 
the seismic requirements of Ref. 9.14-16 except 
that the design input forces shall be modified in 
the same manner shown in Section 9.14.7.3.7.1 of 
this Standard. 



Minimum Design Loads for Buildings and Other Structures 



199 



9.14.73.7.3 Reinforced and Prestressed Con- 
crete. Reinforced and prestressed concrete tanks 
shall be designed in accordance with the seismic 
requirements of Ref. 9.14-3 except that the design 
input forces for allowable stress design procedures 
shall be modified as follows: 

a. For Tj < T 0i and 7y > T s , substitute the 
term S a Ii\AR, where S a is defined in 
Section 9.4.1.2.6, Subsections 1, 2, or 3, for 
the terms in the appropriate equations as 
shown below: 

ZIC X 

For shear and overturning 

R\ 

moment equations of Ref. 9.14-17 
ZIC X 



For 



Ry 



shear and overturning 



moment equations of Ref. 9.14-18 

zisct 



For 



Ri 



in the base shear and 



overturning moment equations of 
Ref. 9.14-3 

b. For T < Tj < T s , substitute the term 

Z/Ci ZlSd 

for terms and 



SpsI 

1AR 



R\ 



Ri 



c. For all values of T c (or T w ), 



ZIC C 



ZIC C ZISC C 

and are replaced by 

R\v Re 

6Sdi 6$ ds I 



where 



or 



T} 



Ts 



Sa> Sdi, Sds, To, and T s are defined in 
Section 9.4.1.2.6 of this Standard. 

9.14.7.3.8 Petrochemical and Industrial Tanks and 
Vessels Storing Liquids. 

9.14.7.3.8.1 Welded Steel. Welded steel petro- 
chemical and industrial tanks and vessels storing 
liquids shall be designed in accordance with the 
seismic requirements of Ref. 9.14-6 and Ref. 9.14- 
7 except that the design input forces for allow- 
able stress design procedures shall be modified 
as follows: 

a. When using the equations in Section E.3 
of Ref. 9.14-7, substitute into the equation 
for overturning moment M (where S DS and 
T s are defined in Section 9.4.1.2.5 of this 
Standard). Thus, 



In the range T s < T c < 4.0 sec, 

M = S DS I[0.24(W S X S + W t H t + W X X,) 
+ QMC 2 T S W 2 X 2 ] 

(Eq. 9.14.7.3.8.1-1) 

0.755 

where C? = and S — 1.0 

T c 

In the range T w > 4.0 sec, and 

M = S DS I[0.2A(W S X S + W t H t + WiX x ) 

+ 0J\C 2 T s W 2 X 2 ] 

(Eq. 9.14.7.3.8.1-2) 

3,3755 
where C 2 = ~ — and S = 1.0 

c 

9.14.7.3.8.2 Bolted Steel Bolted steel tanks used 
for storage of production liquids. Ref. 9.14-10 cov- 
ers the material, design, and erection requirements 
for vertical, cylindrical, aboveground bolted tanks 
in nominal capacities of 100 to 10,000 barrels for 
production service. Unless required by the building 
official having jurisdiction, these temporary struc- 
tures need not be designed for seismic loads. If 
design for seismic load is required, the loads may 
be adjusted for the temporary nature of the antici- 
pated service life. 

9.14.7.3.8.3 Reinforced and Prestressed Con- 
crete. Reinforced concrete tanks for the storage 
of petrochemical and industrial liquids shall be 
designed in accordance with the force requirements 
of Section 14.7.3.7.3. 

9.14.7.3.9 Ground-Supported Storage Tanks for 
Granular Materials. 

9.14.7.3.9.1 General. The intergranular behavior 
of the material shall be considered in determin- 
ing effective mass and load paths, including the 
following behaviors: 

a. Increased lateral pressure (and the resulting 
hoop stress) due to. loss of the intergranu- 
lar friction of the material during the seis- 
mic shaking. 

b. Increased hoop stresses generated from tem- 
perature changes in the shell after the mate- 
rial has been compacted. 

c. Intergranular friction, which can transfer 
seismic shear directly to the foundation. 

9.14.7.3.9.2 Lateral Force Determination. The 
lateral forces for tanks and vessels storing granular 



200 



ASCE 7-02 



materials at grade shall be determined by the 
requirements and accelerations for short period 
structures (i.e., Sds)- 

9.14.7.3.9.3 'Force Distribution to Shell and 
Foundation. 

9.14.7.3.9.3.1 Increased Lateral Pressure. The 
increase in lateral pressure on the tank wall shall 
be added to the static design lateral pressure 
but shall not be used in the determination of 
pressure stability effects on the axial buckling 
strength of the tank shell. 

9.14.7.3.9.3.2 Effective Mass. A portion of a 
stored granular mass will act with the shell (the 
effective mass). The effective mass is related to 
the physical characteristics of the product, the 
height-to-diameter (H/D) ratio of the tank, and 
the intensity of the seismic event. The effective 
mass shall be used to determine the shear and 
overturning loads resisted by the tank. 

9.14.7.3.9.3.3 Effective Density. The effective 
density factor (that part of the total stored mass 
of product which is accelerated by the seismic 
event) shall be determined in accordance with 
Ref. 9.14-2. 

9.14.7.3.9.3.4 Lateral Sliding. For granular 
storage tanks that have a steel bottom and 
are supported such that friction at the bottom 
to foundation interface can resist lateral shear 
loads, no additional anchorage to prevent slid- 
ing is required. For tanks without steel bottoms 
(i.e., the material rests directly on the foun- 
dation), shear anchorage shall be provided to 
prevent sliding. 

9.14.7.3.9.3.5 Combined Anchorage Systems. 
If separate anchorage systems are used to pre- 
vent overturning and sliding, the relative stiff- 
ness of the systems shall be considered in deter- 
mining the load distribution. 

9.14.7.3.9.4 Welded Steel Structures. Welded 
steel granular storage structures shall be designed 
in accordance with Section 9 of this Standard. 
Component allowable stresses and materials shall 
be per Ref. 9.14-15, except the allowable circum- 
ferential membrane stresses and material require- 
ments in Ref. 9.14-7 shall apply. 

9.14.7.3.9.5 Bolted Steel Structures. Bolted steel 
granular storage structures shall be designed in 



accordance with Section 9. Component allowable 
stresses and materials shall be per Ref. 9.14-16. 

9.14.7.3.9.6 Reinforced Concrete Structures. 
Reinforced concrete structures for the storage of 
granular materials shall be designed in accordance 
with the force requirements of Section 9 and the 
requirements of Ref . 9.14-2. 

9.14.7.3.9.7 Prestressed Concrete Structures. 
Prestressed concrete structures for the storage of 
granular materials shall be designed in accordance 
with the force provisions of Section 9 of this 
Standard and the requirements of Ref. 9.14-2. 

9.14.7.3.10 Elevated Tanks and Vessels for Liquids 
and Granular Materials. 

9.14.7.3.10.1 General. This section applies to 
tanks, vessels, bins, and hoppers that are elevated 
above grade where the supporting tower is an inte- 
gral part of the structure, or where the primary 
function of the tower is to support the tank or ves- 
sel. Tanks and vessels that are supported within 
buildings, or are incidental to the primary function 
of the tower, are considered mechanical equip- 
ment and shall be designed in accordance with 
Section 9.6 of this Standard. 

Elevated tanks shall be designed for the force 
and displacement requirements of the applicable 
approved standard, or Section 9.14.5. 

9.14.7.3.10.2 Effective Mass. The design of the 
supporting tower or pedestal, anchorage, and foun- 
dation for seismic overturning shall assume the 
material stored is a rigid mass acting at the vol- 
umetric center of gravity. The effects of fluid- 
structure interaction may be considered in deter- 
mining the forces, effective period, and mass cen- 
troids of the system if the following requirements 
are met: 

a. The sloshing period, T c , is greater than 3T 
where T = natural period of the tank with 
confined liquid (rigid mass) and support- 
ing structure. 

b. The sloshing mechanism (i.e., the percentage 
of convective mass and centroid) is deter- 
mined for the specific configuration of the 
container by detailed fluid- structure interac- 
tion analysis or testing. 

Soil-structure interaction may be included 
in determining T providing the provisions of 
Section 9.5.9 are met. 



Minimum Design Loads for Buildings and Other Structures 



201 



9.14.7.3.10.3 P -Delta Effects. The lateral drift of 
the elevated tank shall be considered as follows: 

a. The design drift, the elastic lateral displace- 
ment of the stored mass center of grav- 
ity shall be increased by the factor, Cd for 
evaluating the additional load in the sup- 
port structure. 

b. The base of the tank shall be assumed to be 
fixed rotationally and laterally. 

c. Deflections due to bending, axial tension, 
or compression shall be considered. For 
pedestal tanks with a height-to-diameter 
ratio less than 5, shear deformations of the 
pedestal shall be considered. 

d. The dead load effects of roof-mounted equip- 
ment or platforms shall be included in 
the analysis. 

e. If constructed within the plumbness toler- 
ances specified by the approved standard, 
initial tilt need not be considered in the P- 
delta analysis. 

9.14.7.3.10.4 Transfer of Lateral Forces into 
Support Tower. For post- supported tanks and 
vessels which are cross-braced: 

a. The bracing shall be installed in such a 
manner as to provide uniform resistance to 
the lateral load (e.g., pretensioning or tuning 
to attain equal sag). 

b. The additional load in the brace due to 
the eccentricity between the post to tank 
attachment and the line of action of the 
bracing shall be included. 

c. Eccentricity of compression strut line of 
action (elements that resist the tensile pull 
from the bracing rods in the lateral-force- 
resisting systems) with their attachment 
points shall be considered. 

d. The connection of the post or leg with 
the foundation shall be designed to resist 
both the vertical and lateral resultant from 
the yield load in the bracing assuming the 
direction of the lateral load is oriented to 
produce the maximum lateral shear at the 
post to foundation interface. Where multiple 
rods are connected to the same location, the 
anchorage shall be designed to resist the 
concurrent tensile loads in the braces. 

9.14.7.3.10.5 Evaluation of Structures Sensitive 
to Buckling Failure. Shell structures that sup- 
port substantial loads may exhibit a primary mode 



of failure from localized or general buckling of 
the support pedestal or skirt during seismic loads. 
Such structures may include single-pedestal water 
towers, skirt- supported process vessels, and sim- 
ilar single-member towers. Where the structural 
assessment concludes that buckling of the support 
is the governing primary mode of failure, structures 
and components in Seismic Use Group III shall be 
designed to resist the seismic forces as follows: 

a. The seismic response coefficient for this 
evaluation shall be per Section 9.5.3.2.1 of 
this Standard with I/R set equal to 1.0. 
Soil-structure and fluid-structure interaction 
may be utilized in determining the structural 
response. Vertical or orthogonal combina- 
tions need not be considered. 

b. The resistance of the structure or component 
shall be defined as the critical buckling 
resistance of the element; i.e., a factor of 
safety set equal to 1.0 

c. The anchorage and foundation shall be 
designed to resist the load determined in (a). 
The foundation shall be proportioned to pro- 
vide a stability ratio of at least 1.2 for 
the overturning moment. The maximum toe 
pressure under the foundation shall not 
exceed the lesser of the ultimate bearing 
capacity or 3 times the allowable bearing 
capacity. All structural components and ele- 
ments of the foundation shall be designed to 
resist the combined loads with a load factor 
of 1.0 on all loads including dead load, live 
load, and earthquake load. Anchors shall be 
permitted to yield. 



9.14.7.3.10.6 Welded Steel Water Storage Struc- 
tures. Welded steel elevated water storage struc- 
tures shall be designed and detailed in accordance 
with the seismic requirements of Ref. 9.14-15 and 
this Standard except that the design input forces 
for allowable stress design procedures shall be 
modified by substituting the following terms for 
ZIC/R W into Eqs. 13-1 and 13-3 of Ref . 9.14-15 
and set the value for S — 1.0. 
For T <Ts, substitute the term 



Sp$I 

IAR 



(Eq. 9.14.7.3.10.6-1) 



For Ts < T < 4.0 second, substitute the term 
Soil 



T(IAR) 



(Eq. 9.14.7.3.10.6-2) 



202 



ASCE 7-02 



For T > 4.0 second, substitute the term 
Soil 



T 2 (IAR) 



(Eq. 9.14.7.3.10.6-3) 



9.14.7.3.10.6.1 Analysis Procedures. The 
equivalent lateral force procedure shall be per- 
mitted. A more rigorous analysis shall also be 
permitted. Analysis of single-pedestal structures 
shall be based on a fixed-base, single degree-of- 
freedom model. All mass, including the liquid, 
shall be considered rigid unless the sloshing 
mechanism (i.e., the percentage of convective 
mass and centroid) is determined for the spe- 
cific configuration of the container by detailed 
fluid- structure interaction analysis or testing. 
The inclusion of soil- structure interaction shall 
be permitted. 

9.14.7.3.10.6.2 Structure Period. The funda- 
mental period of vibration of the structure 
shall be established using the structural prop- 
erties and deformational characteristics of the 
resisting elements in a substantiated analy- 
sis. The period used to calculate the seismic 
response coefficient shall not exceed 4.0 sees. 
See Ref. 9.14-15 for guidance on computing the 
fundamental period of cross-braced structures. 

9.14.7.3.10.7 Concrete Pedestal (Composite) 
Tanks. Concrete pedestal (composite) elevated 
water storage structures shall be designed in 
accordance with the requirements of Ref. 9.14-4 
except that the design input forces shall be 
modified as follows: 

InEq. 4-8aof Ref. 9.14-4, 

For Ts < T < 4.0 sec, replace the term \2C v i 
RT 1 ^ with 



TR 



(Eq. 9,14.7.3.10.7-1) 



For T > 4.0 sec, replace the term \2C y /RT 2 ^ 

With AS I 

— ^» (Eq. 9.14.7.3.10.7-2) 

T 2 R H 

In Eq. 4-8b of Ref. 9.14-4, replace the term 
2.5C a /R with 



SpsI 
R 



(Eq. 9.14.7.3.10.7-3) 



In Eq. 4-9 of Ref. 9.14-4, replace the term 
0.5C a with 

0.2S D5 (Eq. 9.14.7.3.10.7-4) 

Minimum Design Loads for Buildings and Other Structures 



9.14.7.3.10.7.1 Analysis Procedures. The 
equivalent lateral force procedure shall be per- 
mitted for all concrete pedestal tanks and shall 
be based on a fixed-base, single degree-of- 
freedom model. All mass, including the liquid, 
shall be considered rigid unless the sloshing 
mechanism (i.e., the percentage of convective 
mass and centroid) is determined for the specific 
configuration of the container by detailed fluid- 
structure interaction analysis or testing. Soil- 
structure interaction may be included. A more 
rigorous analysis shall be permitted. 

9.14.7.3.10.7.2 Structure Period. The funda- 
mental period of vibration of the structure shall 
be established using the uncracked structural 
properties and deformational characteristics of 
the resisting elements in a properly substanti- 
ated analysis. The period used to calculate the 
seismic response coefficient shall not exceed 
2.5 sec. 

9.14.7.3.11 Boilers and Pressure Vessels. 

9.14.7.3.11.1 General. Attachments to the pres- 
sure boundary, supports, and lateral-force-resisting 
anchorage systems for boilers and pressure vessels 
shall be designed to meet the force and displace- 
ment requirements of Sections 9.5.5 and 9.5.6 and 
the additional requirements of this section. Boilers 
and pressure vessels categorized as Seismic Use 
Group III or III shall be designed to meet the force 
and displacement requirements of Sections 9.5.5 
and 9.5.6. 

9.14.7.3.11.2 ASME Boilers and Pressure Ves- 
sels. Boilers or pressure vessels designed and 
constructed in accordance with Ref. 9.14-11 shall 
be deemed to meet the requirements of this section 
provided that the displacement requirements of 
Sections 9.5.5 and 9.5.6 are used with appropriate 
scaling of the force and displacement requirements 
to the working stress design basis. 

9.14.7.3.11.3 Attachments of Internal Equip- 
ment and Refractory. Attachments to the pres- 
sure boundary for internal and external ancillary 
components (refractory, cyclones, trays, etc.) shall 
be designed to resist the seismic forces speci- 
fied in this Standard to safeguard against rupture 
of the pressure boundary. Alternatively, the ele- 
ment attached may be designed to fail prior to 
damaging the pressure boundary provided that the 
consequences of the failure do not place the pres- 
sure boundary in jeopardy. For boilers or vessels 



203 



containing liquids, the effect of sloshing on the 
internal equipment shall be considered if the equip- 
ment can damage the integrity of the pressure 
boundary. 

9.14.73.11.4 Coupling of Vessel and Support 
Structure. Where the mass of the operating vessel 
or vessels supported is greater than 25% of the total 
mass of the combined structure, the structure and 
vessel designs shall consider the effects of dynamic 
coupling between each other. Coupling with adja- 
cent, connected structures such as multiple towers 
shall be considered if the structures are intercon- 
nected with elements that will transfer loads from 
one structure to the other. 

9.14.7.3.11.5 Effective Mass. Fluid-structure inte- 
raction (sloshing) shall be considered in determin- 
ing the effective mass of the stored material pro- 
viding sufficient liquid surface exists for sloshing 
to occur and the T c is greater than 37\ Changes to 
or variations in material density with pressure and 
temperature shall be considered. 

9.14.7.3.11.6 Other Boilers and Pressure Ves- 
sels. Boilers and pressure vessels designated Seis- 
mic Use Group III but not designed and con- 
structed in accordance with the requirements of 
Ref. 9.14-11 shall meet the following require- 
ments: 

The seismic loads in combination with other 
service loads and appropriate environmental effects 
shall not exceed the material strength shown in 
Table 9.14.7.3.11.6. 

Consideration shall be made to mitigate seismic 
impact loads for boiler or vessel components con- 
structed of nonductile materials or vessels operated 

TABLE 9.14.7.3.11.6 
MAXIMUM MATERIAL STRENGTH 



Material 


Minimum 
Ratio 

FulFy 


Max Material 

Strength 

Vessel Material 


Max Material 
Strength 
Threaded 
Material 3 


Ductile (e.g., steel, 
aluminum, copper) 


1.33 b 


90% d 


70% d 


Semiductile 


1.2 C 


70% d 


50% d 


Nonductile (e.g., cast 
iron, ceramics, 
fiberglass) 


NA 


25 % e 


20% e 



a Threaded connection to vessel or support system. 

b Minimum 20% elongation per the ASTM material specification. 

c Minimum 15% elongation per the ASTM material specification. 

d Based on material minimum specified yield strength. 

e Based on material minimum specified tensile strength. 



in such a way that material ductility is reduced 
(e.g., low-temperature applications). 

9.14.7.3,1 1.7 Supports and Attachments for 

Boilers and Pressure Vessels. Attachments to 
the pressure boundary and support for boilers 
and pressure vessels shall meet the following 
requirements: 

a. Attachments and supports transferring seis- 
mic loads shall be constructed of ductile 
materials suitable for the intended applica- 
tion and environmental conditions. 

b. Seismic anchorages embedded in concrete 
shall be ductile and detailed for cyclic loads. 

c. Seismic supports and attachments to struc- 
tures shall be designed and constructed so 
that the support or attachment remains duc- 
tile throughout the range of reversing seismic 
lateral loads and displacements. 

d. Vessel attachments shall consider the poten- 
tial effect on the vessel and the support for 
uneven vertical reactions based on variations 
in relative stiffness of the support members, 
dissimilar details, nonuniform shimming, or 
irregular supports. Uneven distribution of 
lateral forces shall consider the relative dis- 
tribution of the resisting elements, the behav- 
ior of the connection details, and vessel shear 
distribution. 

The requirements of Sections 9.14.5 and 
9.14.7.3.10.5 shall also be applicable to this 
section. 

9.14.7.3.12 Liquid and Gas Spheres. 

9.14.7.3.12.1 General. Attachments to the pres- 
sure or liquid boundary, supports, and lateral- 
force-resisting anchorage systems for liquid and 
gas spheres shall be designed to meet the force 
and displacement requirements of Sections 9.5.5 
and 9.5.6 and the additional requirements of 
this section. Spheres categorized as Seismic Use 
Group III or III shall themselves be designed to 
meet the force and displacement requirements of 
Sections 9.5.5 and 9.5.6. 

9.14.7.3.12.2 ASHE Spheres. Spheres designed 
and constructed in accordance with Section VIII 
of Ref. 9.14-11 shall be deemed to meet the 
requirements of this section providing the displace- 
ment requirements of Sections 9.5.5 and 9.5.6 are 
used with appropriate scaling of the force and 
displacement requirements to the working stress 
design basis. 



204 



ASCE 7-02 



9.14.7.3.12.3 Attachments of Internal Equip- 
ment and Refractory. Attachments to the pressure 
or liquid boundary for internal and external ancil- 
lary components (refractory, cyclones, trays, and 
so on) shall be designed to resist the seismic forces 
specified in this Standard to safeguard against rup- 
ture of the pressure boundary. Alternatively, the 
element attached to the sphere could be designed 
to fail prior to damaging the pressure or liquid 
boundary providing the consequences of the fail- 
ure do not place the pressure boundary in jeopardy. 
For spheres containing liquids, the effect of slosh- 
ing on the internal equipment shall be considered if 
the equipment can damage the pressure boundary. 

9.14.7.3.12.4 Effective Mass. Fluid-structure 
interaction (sloshing) shall be considered in deter- 
mining the effective mass of the stored material 
providing sufficient liquid surface exists for slosh- 
ing to occur and the T c is greater than 37\ Changes 
to or variations in fluid density shall be considered. 

9.14.7.3.12.5 Post and Rod Supported. For post- 
supported spheres that are cross-braced: 

a. The requirements of Section 9.14.7.3.10.4 
shall also be applicable to this section. 

b. The stiffening effect of (reduction in lat- 
eral drift) from pre-tensioning of the bracing 
shall be considered in determining the natu- 
ral period. 

c. The slenderness and local buckling of the 
posts shall be considered. 

d. Local buckling of the sphere shell at the post 
attachment shall be considered. 

e. For spheres storing liquids, bracing con- 
nections shall be designed and constructed 
to develop the minimum published yield 
strength of the brace. For spheres storing 
gas vapors only, bracing connection shall be 
designed for Q a times the maximum design 
load in the brace. Lateral bracing connections 
directly attached to the pressure or liquid 
boundary are prohibited. 

9.14.73.12.6 Skirt Supported. For skirt-suppor- 
ted spheres, the following requirements shall 
apply: 

a. The provisions of Section 9.14.7.3.10.5 shall 
also apply, 

b. The local buckling of the skirt under com- 
pressive membrane forces due to axial load 
and bending moments shall be considered. 



c. Penetration of the skirt support (manholes, 
piping, and so on) shall be designed and 
constructed to maintain the strength of the 
skirt without penetrations. 

9.14.7.3.13 Refrigerated Gas Liquid Storage Tanks 
and Vessels. 

9.14.7.3.13.1 General. The seismic design of the 
tanks and facilities for the storage of liquefied 
hydrocarbons and refrigerated liquids is beyond the 
scope of this section. The design of such tanks is 
addressed in part by various approved standards as 
listed in Table 9.14.3. 

Exception: Low-pressure, welded steel storage 
tanks for liquefied hydrocarbon gas (e.g., LPG, 
butane, and so on) and refrigerated liquids 
(e.g., ammonia) shall be designed in accordance 
with the requirements of Section 9.14.7.3.8 and 
Ref. 9.14-6. 

9.14.7.3.14 Horizontal, Saddle-Supported Vessels 
for Liquid or Vapor Storage. 

9.14.7.3.14.1 General. Horizontal vessels sup- 
ported on saddles (sometimes referred to as 
blimps) shall be designed to meet the force 
and displacement requirements of Sections 9.5.5 
and 9.5.6. 

9.14.7.3.14.2 Effective Mass. Changes to or vari- 
ations in material density shall be considered. The 
design of the supports, saddles, anchorage, and 
foundation for seismic overturning shall assume 
the material stored is a rigid mass acting at the 
volumetric center of gravity. 

9.14.7.3.14.3 Vessel Design. Unless a more rigor- 
ous analysis is performed: 

a. Horizontal vessels with a length-to-diameter 
ratio of 6 or more may be assumed to be a 
simply supported beam spanning between the 
saddles for determining the natural period of 
vibration and global bending moment. 

b. Horizontal vessels with a length-to-diameter 
ratio of less than 6, the effects of "deep beam 
shear" shall be considered when determining 
the fundamental period and stress distribu- 
tion. 

c. Local bending and buckling of the vessel 
shell at the saddle supports due to seis- 
mic load shall be considered. The stabilizing 



Minimum Design Loads for Buildings and Other Structures 



205 



effects of internal pressure shall not be con- 
sidered to increase the buckling resistance of 
the vessel shell. 

d. If the vessel is a combination of liquid 
and gas storage, the vessel and supports 
shall be designed both with and without gas 
pressure acting (assume piping has ruptured 
and pressure does not exist). 

9.14.7.4 Stacks and Chimneys. 

9.14.7.4.1 General. Stacks and chimneys are permit- 
ted to be either lined or unlined, and shall be con- 
structed from concrete, steel, or masonry. 

9.14.7.4.2 Design Basis. Steel stacks, concrete stacks, 
steel chimneys, concrete chimneys, and liners shall 
be designed to resist seismic lateral forces deter- 
mined from a substantiated analysis using approved 
standards. Interaction of the stack or chimney with 
the liners shall be considered. A minimum separation 
shall be provided between the liner and chimney equal 
to Q times the calculated differential lateral drift. 

9.14.7.5 Amusement Structures. 

9.14.7.5.1 General. Amusement structures are per- 
manently fixed structures constructed primarily for 
the conveyance and entertainment of people. 

9.14.7.5.2 Design Basis. Amusement structures shall 
be designed to resist seismic lateral forces deter- 
mined from a substantiated analysis using approved 
standards. 

9.14.7.6 Special Hydraulic Structures. 

9.14.7.6.1 General. Special hydraulic structures are 
structures that are contained inside liquid-containing 
structures. These structures are exposed to liquids 
on both wall surfaces at the same head elevation 
under normal operating conditions. Special hydraulic 
structures are subjected to out-of-plane forces only 
during an earthquake when the structure is subjected 
to differential hydrodynamic fluid forces. Examples of 
special hydraulic structures include separation walls, 
baffle walls, weirs, and other similar structures. 

9.14.7.6.2 Design Basis. Special hydraulic structures 
shall be designed for out-of-phase movement of the 
fluid. Unbalanced forces from the motion of the liquid 
must be applied simultaneously "in front of and 
"behind" these elements. 



Structures subject to hydrodynamic pressures 
induced by earthquakes shall be designed for rigid 
body and sloshing liquid forces and their own inertia 
force. The height of sloshing shall be determined and 
compared to the freeboard height of the structure. 

Interior elements, such as baffles or roof supports, 
also shall be designed for the effects of unbalanced 
forces and sloshing. 

9.14.7,7 Secondary Containment Systems. Secondary 
containment systems such as impoundment dikes and 
walls shall meet the requirements of the applicable 
standards for tanks and vessels and the authority having 
jurisdiction. 

Secondary containment systems shall be designed to 
withstand the effects of the maximum considered earth- 
quake ground motion when empty and two-thirds of the 
maximum considered earthquake ground motion when 
full including all hydrodynamic forces as determined 
in accordance with the procedures of Section 9.4,1. 
When determined by the risk assessment required by 
Section 1.5.2 or by the authority having jurisdiction that 
the site may be subject to aftershocks of the same mag- 
nitude as the maximum considered ground motion, sec- 
ondary containment systems shall be designed to with- 
stand the effects of the maximum considered earthquake 
ground motion when full including all hydrodynamic 
forces as determined in accordance with the procedures 
of Section 9.4.1. 

9.14.7.7.2 Freeboard. Sloshing of the liquid within 
the secondary containment area shall be considered 
in determining the height of the impound. Where the 
primary containment has not been designed with a 
reduction in the structure category (i.e., no reduction 
in importance factor I) as permitted by Section 1.5.2, 
no freeboard provision is required. Where the primary 
containment has been designed for a reduced structure 
category (i.e., importance factor I reduced) as permit- 
ted by Section 1.5.2, a minimum freeboard, 8 S , shall 
be provided where 



S s = 0.50DS a 



(Eq. 9.14.7.7.2) 



where S ac is the spectral acceleration of the convec- 
tive component and is determined according to the 
procedures of Section 9.4.1 using 0.5% damping. For 
circular impoundment dikes, D shall be taken as the 
diameter of the impoundment dike. For rectangular 
impoundment dikes, D shall be taken as the longer 
plan dimension of the impoundment dike. 

9.14.7.8 Telecommunication Towers. Self-supporting 
and guyed telecommunication towers shall be designed 
to resist seismic lateral forces determined from a sub- 
stantiated analysis using approved standards. 



206 



ASCE 7-02 



SECTION 10.0 

ICE LOADS - ATMOSPHERIC ICING 



SECTION 10.1 
GENERAL 

Atmospheric ice loads due to freezing rain, snow, and in- 
cloud icing shall be considered in the design of ice-sensitive 
structures. In areas where records or experience indicate 
that snow or in-cloud icing produces larger loads than 
freezing rain, site-specific studies shall be used. Structural 
loads due to hoarfrost are not a design consideration. Roof 
snow loads are covered in Section 7. 

10.1.1 Site-Specific Studies, Mountainous terrain and gor- 
ges shall be examined for unusual icing conditions. Site- 
specific studies shall be used to determine the 50-year 
mean recurrence interval ice thickness and concurrent wind 
speed in: 

1. Alaska. 

2. areas where records or experience indicate that snow 
or in-cloud icing produces larger loads than freez- 
ing rain. 

3. special icing regions shown in Figure 10-2. 

4. mountainous terrain and gorges where examination 
indicates unusual icing conditions exist. 

Site-specific studies shall be subject to review and 
approval by the authority having jurisdiction. 

In lieu of using the mapped values, it shall be permitted 
to determine the ice thickness and the concurrent wind 
speed for a structure from local meteorological data based 
on a 50-year mean recurrence interval provided that: 

1 . the quality of the data for wind and type and amount 
of precipitation has been taken into account, 

2. a robust ice accretion algorithm has been used to 
estimate uniform ice thicknesses and concurrent wind 
speeds from these data, 

3. extreme- value statistical analysis procedures accept- 
able to the authority having jurisdiction have been 
employed in analyzing the ice thickness and concur- 
rent wind speed data, and 

4. the length of record and sampling error have been 
taken into account. 

10.1.2 Dynamic Loads* Dynamic loads, such as those 
resulting from galloping, ice shedding, and aeolian vibra- 
tions, that are caused or enhanced by an ice accretion on 
a flexible structural member, component, or appurtenance 
are not covered in this Section. 



10.1.3 Exclusions. Electric transmission systems, commu- 
nications towers and masts, and other structures for which 
national standards exist are excluded from the requirements 
of this section. Applicable standards and guidelines include 
Refs. 10-1, 10-2, and 10-3. 



SECTION 10.2 
DEFINITIONS 

The following definitions apply only to the provisions of 
Section 10. 

COMPONENTS AND APPURTENANCES. Nonstruc- 
tural elements that may be exposed to atmospheric icing. 
Examples are ladders, handrails, antennas, waveguides, 
radio frequency (RF) transmission lines, pipes, electrical 
conduits, and cable trays. 

FREEZING RAIN. Rain or drizzle that falls into a layer 
of subfreezing air at the earth's surface and freezes on 
contact with the ground or an object to form glaze ice. 

GLAZE. Clear high-density ice. 

HOARFROST. An accumulation of ice crystals formed by 
direct deposition of water vapor from the air onto an object. 

ICE-SENSITIVE STRUCTURES. Structures for which 
the effect of an atmospheric icing load governs the design of 
part or all of the structure. This includes, but is not limited 
to, lattice structures, guyed masts, overhead lines, light 
suspension and cable-stayed bridges, aerial cable systems 
(e.g., for ski lifts and logging operations), amusement rides, 
open catwalks and platforms, flagpoles, and signs. 

IN-CLOUD ICING. Occurs when supercooled cloud or 
fog droplets carried by the wind freeze on impact with 
objects. In-cloud icing usually forms rime but may also 
form glaze. 

RIME. White or opaque ice with entrapped air. 

SNOW. Snow that adheres to objects by some combination 
of capillary forces, freezing, and sintering. 



SECTION 10.3 
SYMBOLS AND NOTATION 

A s = surface area of one side of a flat plate or the 
projected area of complex shapes 



Minimum Design Loads for Buildings and Other Structures 



207 



A t — cross- sectional area of ice 

D — diameter of a circular structure or member as 

defined in Section 6, in ft (m) 
D c = diameter of the cylinder circumscribing an object 
f z — factor to account for the increase in ice thickness 

with height 
Ii = importance factor and multiplier on ice thickness 

based on the structure category as defined in 

Section 1 
I w — importance factor and multiplier on the concurrent 

wind pressure based on the structure category as 

defined in Section 1 
K zt — topographic factor as defined in Section 6 
q z = velocity pressure evaluated at height z above 

ground, in lb/ft 2 (N/m 2 ) as defined in Section 6 
r = radius of the maximum cross-section of a dome or 

radius of a sphere 
t = nominal ice thickness due to freezing rain at a 

height of 33 ft (10 m) from Figure 10-2, 10-3, or 

10-4 in in. (mm) 
td = design ice thickness in in. (mm) from Eq. 10-5 
V c = concurrent wind speed mph (m/s) from 

Figures 10-2, 10-3, and 10-4 
Vj — volume of ice 
z = height above ground in ft (m) 
e = solidity ratio as defined in Section 6 



SECTION 10.4 
ICE LOADS DUE TO FREEZING RAIN 

10*4.1 Ice Weight. The ice load shall be determined using 
the weight of glaze ice formed on all exposed surfaces of 
structural members, guys, components, appurtenances, and 
cable systems. On structural shapes, prismatic members, 
and other similar shapes, the cross-sectional area of ice 
shall be determined by: 



A t =7tt d (D c + t d ) 



(Eq. 10-1) 



D c is shown for a variety of cross- sectional shapes in 
Figure 10-1. 

On flat plates and large three-dimensional objects such 
as domes and spheres, the volume of ice shall be deter- 
mined by: 

V t = 7it d A s (Eq. 10-2) 

For a flat plate A s shall be the area of one side of the plate, 
for domes and spheres A s shall be determined by: 



A, = ixr 



(Eq. 10-3) 



It is acceptable to multiply V/ by 0.8 for vertical plates and 
0.6 for horizontal plates. 

The ice density shall be not less than 56 pcf (900 kg/m 3 ). 



10.4.2 Nominal Ice Thickness. Figures 10-2, 10-3, and 
10-4 show the equivalent uniform radial thicknesses t of 
ice due to freezing rain at a height of 33 ft (10 m) over 
the contiguous United States for a 50-year mean recurrence 
interval. Also shown are concurrent 3-second gust wind 
speeds. Thicknesses for Alaska and Hawaii, and for ice 
accretions due to other sources in all regions, shall be 
obtained from local meteorological studies. 

10.4.3 Height Factor. The height factor f z used to 
increase the radial thickness of ice for height above ground 
z shall be determined by: 

f z = (—\ H for ft < z < 900 ft (Eq. 10-4) 



/ z = 1.4 for z>900ft 



In SI 



,0.10 



f z = (— ) for m < z < 275 m 
/ e = 1.4 for z > 275 m 

10.4.4 Importance Factors. Importance factors to be 
applied to the radial ice thickness and wind pressure accord- 
ing to the structure classifications (as defined in Table 1-1) 
are listed in Table 10-1. The importance factor multiplier 
/( must be on the ice thickness, not the ice weight because 
the ice weight is not a linear function of thickness. 

10.4.5 Topographic Factor, Both the ice thickness and 
concurrent wind speed for structures on hills, ridges, and 
escarpments are higher than those on level terrain because 
of wind speed-up effects. The topographic factor for the 
concurrent wind pressure is K zt and the topographic factor 
for ice thickness is (K zt ) 035 , where K zt is obtained from 
Eq. 6-1. 

10.4.6 Design Ice Thickness for Freezing Rain. The 
design ice thickness t d shall be calculated from Eq. 10-5. 



t d =2.0tIif z (K zt y 



0.35 



(Eq. 10-5) 



SECTION 10,5 
WIND ON ICE-COVERED STRUCTURES 

Ice accreted on structural members, components, and appur- 
tenances increases the projected area of the structure 
exposed to wind. The projected area shall be increased 
by adding t d to all free edges of the projected area. Wind 
loads on this increased projected area shall be used in the 
design of ice-sensitive structures. Figures 10-2, 10-3, and 
10-4 include 3-second gust wind speeds at 33 ft (10 m) 



208 



ASCE 7-02 



above grade that are concurrent with the ice loads due 
to freezing rain. Wind loads shall be calculated in accor- 
dance with Section 6 as modified by Sections 10.5.1 to 
10.5.4 below. 

10.5.1 Wind on Ice-Covered Chimneys, Tanks, and 
Similar Structures. Force coefficients for structures with 
square, hexagonal, and octagonal cross-sections shall be 
as given in Table 6-19. Force coefficients for structures 
with round cross-sections shall be as given in Table 6-19 
for round cross-sections with Dy/q z < 2.5 for all ice 
thicknesses, wind speeds, and structure diameters. 

1.0.5.2 Wind on Ice-Covered Solid Freestanding Walls 
and Solid Signs. Force coefficients shall be as given in 
Table 6-10 based on the dimensions of the wall or sign 
including ice. 

10.5.3 Wind on Ice-Covered Open Signs and Lattice 
Frameworks. The solidity ratio e shall be based on the 
projected area including ice. The force coefficient for 
the projected area of flat members shall be as given in 
Table 6-21. The force coefficient for rounded members and 
for the additional projected area due to ice on both flat 
and rounded members shall be as given in Table 6-21 for 
rounded members with Dy/q z < 2.5 for all ice thicknesses, 
wind speeds and member diameters. 

10.5.4 Wind on Ice-Covered Trussed Towers. The solid- 
ity ratio e shall be based on the projected area including ice. 
The force coefficients shall be as given in Table 6-22. It is 
acceptable to reduce the force coefficients for the additional 
projected area due to ice on both round and flat members 
by the factor for rounded members in Note 3 of Table 6-22. 



SECTION 10.6 
PARTIAL LOADING 

The effects of a partial ice load shall be considered when 
this condition is critical for the type of structure under 
consideration. It is permitted to consider this to be a 
static load. 



SECTION 10.7 
DESIGN PROCEDURE 

1. The nominal ice thickness, t, and the concurrent 
wind speed, V C9 for the site shall be determined from 
Figures 10-2, 10-3, 10-4, or a site-specific study. 

2. The topographic factor for the site, K zti shall be 
determined in accordance with Section 10.4.5. 

3. The importance factor, //, shall be determined in 
accordance with Section 10.4.4. 

4. The height factor, f z , shall be determined in accor- 
dance with Section 10.4.3 for each design segment 
of the structure. 

5. The design ice thickness, td, shall be determined in 
accordance with Section 10.4.6, Eq. 10-5. 

6. The weight of ice shall be calculated for the design 
ice thickness, td in accordance with Section 10.4.1. 

7. The velocity pressure q z for wind speed V c shall be 
determined in accordance with Section 6.5.10 using 
I w for the importance factor /. 

8. The wind force coefficients shall be determined in 
accordance with Section 10.5. 

9. The gust effect factor shall be determined in accor- 
dance with Section 6.5.8. 

10. The design wind force shall be determined in 
accordance with Section 6.5.13. 

11. The iced structure shall be analyzed for the load 
combinations in either Section 2.3 or Section 2.4. 



SECTION 10.8 
REFERENCES 

Ref. 10-1 ANSI. (2002). "National Electrical Safety Code." 
(NESC). ANSI C2. 

Ref. 10-2 ASCE. (1991). "Guidelines for Electrical Trans- 
mission Line Structural Loading." ASCE 74. 

Ref. 10-3 ANSI/EIA/TIA. (1996). "Structural Standards 
for Steel Antenna Towers and Antenna Support- 
ing Structures." EIA/TIA-222. 



Minimum Design Loads for Buildings and Other Structures 



209 








FIGURE 10-1 
CHARACTERISTIC DIMENSION "D c " FOR CALCULATING THE ICE AREA FOR A VARIETY OF CROSS-SECTIONAL SHAPES 



210 



ASCE 7-02 



This page intentionally left blank. 



Minimum Design Loads for Buildings and Other Structures 21 1 




Ice Load Zones 
Wind Speed Zones 



Notes 



1 . In the Appalachian Mountains, indicated by the gray fill, 
ice loads may vary significantly over short distances. 

2. Ice loads on structures in exposed locations at elevations 
higher than the surrounding terrain and in valleys and 
gorges may be higher than the mapped loads. 

FIGURE 10-2a 
50-YR MEAN RECURRENCE INTERVAL UNIFORM ICE THICKNESSES DUE TO FREEZING RAIN WITH CONCURRENT 3-s GUST WIND 

SPEEDS: CONTIGUOUS 48 STATES 



212 



ASCE 7-02 




FIGURE 10-2b - continued 



Minimum Design Loads for Buildings and Other Structures 



213 




FIGURE 10-3 

50-YR MEAN RECURRENCE INTERVAL UNIFORM ICE 

THICKNESSES DUE TO FREEZING RAIN WITH CONCURRENT 

3-s GUST WIND SPEEDS: LAKE SUPERIOR 



214 



ASCE 7-02 




Motes: 

1. Ice thickness is shown in inches. 

2. Unless otherwise specified use 0.50 inch ice thicknesses. 

3. Freezing rain is unlikely to occur in the shaded mountainous 
regions above 5,000 feet. 

4. Apply a concurrent 3-sec gust of 50 mph to the 
appropriate ice thicknesses. 



□ 



FIGURE 10-4 
50-YR MEAN RECURRENCE INTERVAL UNIFORM ICE THICKNESSES DUE TO FREEZING RAIN WITH CONCURRENT 3-s GUST WIND 

SPEEDS: PACIFIC NORTHWEST 



Minimum Design Loads for Buildings and Other Structures 



215 



TABLE 10-1 
IMPORTANCE FACTOR /, AND S w 



Structure 
Category 


(Multiplier on Ice 
Thickness) 


(Multiplier on 

Concurrent Wind 

Pressure) 


I 


0.80 


1.0 


II 


1.00 


1.0 


III 


1.25 


1.0 


IV 


1.25 


1.0 



216 



ASCE 7-02 



APPENDIX A.9 

SUPPLEMENTAL PROVISIONS 



SECTION A.9.1 
PURPOSE 

These provisions are not directly related to computation 
of earthquake loads, but they are deemed essential for 
satisfactory performance in an earthquake when designing 
with the loads determined from Section 9, due to the 
substantial cyclic inelastic strain capacity assumed to exist 
by the load procedures in Section 9. These supplemental 
provisions form an integral part of Section 9. 



SECTION A.9.3 
QUALITY ASSURANCE 

This section provides minimum requirements for quality 
assurance for seismic force-resisting systems and other des- 
ignated seismic systems. These requirements supplement 
the testing and inspection requirements contained in the 
reference standards given in Sections 9.6 through 9.12. 

A.9.3.1 Scope. As a minimum, the quality assurance pro- 
visions apply to the following: 

1. The seismic force-resisting systems in structures 
assigned to Seismic Design Categories C, D, E, 
and F. 

2. Other designated seismic systems in structures as- 
signed to Seismic Design Categories D, E, and F that 
are required in Table 9.6.1.7. 

Exception: Structures that comply with the fol- 
lowing criteria are exempt from the preparation of 
a quality assurance plan but those structures are 
not exempt from special inspection(s) or testing 
requirements: 

a. The structure is constructed of light wood framing 
or light-gauge cold-formed steel framing, Sds does 
not exceed 0.50 g, the height of the structure does 
not exceed 35 ft above grade, and the structure 
meets the requirements in Items c and d below, 

or 

b. The structure is constructed using a reinforced 
masonry structural system or reinforced concrete 
structural system, Sos does not exceed 0.50 g, the 
height of the structure does not exceed 25 ft above 
grade, and the structure meets the requirements in 
Items c and d below. 



c. The structure is classified as Seismic Use Group I. 

d. The structure does not have any of the following 
plan irregularities as defined in Table 9.5.2.3.2 
or any of the following vertical irregularities as 
defined in Table 9.5.2.3.3: 

1 . Torsional irregularity 

2. Extreme torsional irregularity 

3. Nonparallel systems 

4. Stiffness irregularity/soft story 

5. Stiffness irregularity /extreme soft story 

6. Discontinuity in capacity /weak story 

The following standards are referenced in the provisions 
for inspection and testing: 

Ref. 9.1.6-1 ANSI. (1998). "Structural Welding Code- 
Steel." ANSI/AWS D1. 1-98. 

Ref. 9.1.6-2 ASTM. (1990). "Specification for Straight 
Beam Ultrasound Examination of Steel 
Plates." ASTM A435-90. 

Ref. 9.1.6-3 ASTM. (1991). "Specification for Straight 
Beam Ultrasound Examination for Rolled 
Steel Shapes." ASTM A898-91. 

A.9.3.2 Quality Assurance Plan. A quality assurance 
plan shall be submitted to the authority having jurisdiction. 

A.9.3.2. 1 Details of Quality Assurance Plan. The 
quality assurance plan shall specify the designated seis- 
mic systems or seismic force-resisting system in accor- 
dance with Section A.9.3 that are subject to quality 
assurance. The registered design professional in respon- 
sible charge of the design of a seismic force-resisting 
system and a designated seismic system shall be respon- 
sible for the portion of the quality assurance plan appli- 
cable to that system. The special inspections and special 
tests needed to establish that the construction is in con- 
formance with these provisions shall be included in the 
portion of the quality assurance plan applicable to the 
designated seismic system. The quality assurance plan 
shall include: 

a. The seismic force-resisting systems and designated 
seismic systems in accordance with this chapter 
that are subject to quality assurance. 

b. The special inspections and testing to be provided 
as required by these provisions and the reference 
standards in Section 9. 



Minimum Design Loads for Buildings and Other Structures 



217 



c. The type and frequency of testing. 

d. The type and frequency of special inspections. 

e. The frequency and distribution of testing and 
special inspection reports. 

f. The structural observations to be performed. 

g. The frequency and distribution of structural obser- 
vation reports. 

A.9.3.2.2 Contractor Responsibility. Each contractor 
responsible for the construction of a seismic force- 
resisting system, designated seismic system, or compo- 
nent listed in the quality assurance plan shall submit 
a written contractor's statement of responsibility to the 
regulatory authority having jurisdiction and to the owner 
prior to the commencement of work on the system or 
component. The contractor's statement of responsibility 
shall contain the following: 

1. Acknowledgment of awareness of the special re- 
quirements contained in the quality assurance plan. 

2. Acknowledgment that control will be exercised 
to obtain conformance with the design documents 
approved by the authority having jurisdiction. 

3. Procedures for exercising control within the con- 
tractor's organization, the method and frequency 
of reporting, and the distribution of the reports. 

4. Identification and qualifications of the person(s) 
exercising such control and their position(s) in the 
organization. 

A.9.3.3 Special Inspection. The building owner shall 
employ a special inspector(s) to observe the construction 
of all designated seismic systems in accordance with the 
quality assurance plan for the following construction work: 

A. 933.1 Foundations. Continuous special inspection 
is required during driving of piles and placement of 
concrete in piers or piles. Periodic special inspection 
is required during construction of drilled piles, piers, 
and caisson work, the placement of concrete in shallow 
foundations, and the placement of reinforcing steel. 

A.9.3.3.2 Reinforcing Steel. 

A.933.2.1 Periodic special inspection during and on 
completion of the placement of reinforcing steel in 
intermediate and special moment frames of concrete 
and concrete shear walls. 

A.933.2.2 Continuous special inspection during 
the welding of reinforcing steel resisting flexural 
and axial forces in intermediate and special moment 
frames of concrete, in boundary members of concrete 
shear walls, and welding of shear reinforcement. 



A.93.33 Structural Concrete. Periodic special in- 
spection during and on completion of the placement of 
concrete in intermediate and special moment frames, and 
in boundary members of concrete shear walls. 

A.933.4 Prestressed Concrete. Periodic special in- 
spection during the placement and after the completion 
of placement of prestressing steel and continuous special 
inspection is required during all stressing and grouting 
operations and during the placement of concrete. 

A.9.3.3.5 Structural Masonry. 

A.933,5.1 Periodic special inspection during the 
preparation of mortar, the laying of masonry units, 
and placement of reinforcement; and prior to place- 
ment of grout. 

A.933.5.2 Continuous special inspection during 
welding of reinforcement, grouting, consolidation and 
reconsolidation, and placement of bent-bar anchors as 
required by Section A.9.11. 

A.9.3.3.6 Structural Steel. 

A.933.6.1 Continuous special inspection is required 
for all structural welding. 

Exception: Periodic special inspection for single- 
pass fillet or resistance welds and welds loaded 
to less than 50% of their design strength shall 
be the minimum requirement, provided the qual- 
ifications of the welder and the welding electrodes 
are inspected at the beginning of the work and 
all welds are inspected for compliance with the 
approved construction documents at the comple- 
tion of welding. 

A.933.6.2 Periodic special inspection is required in 
accordance with Ref. 9.8-1 or 9.8-2 for installation 
and tightening of fully tensioned high-strength bolts 
in slip-critical connections and in connections subject 
to direct tension. Bolts in connections identified as not 
being slip-critical or subject to direct tension need not 
be inspected for bolt tension other than to ensure that 
the plies of the connected elements have been brought 
into snug contact. 

A.933.7 Structural Wood. 

A.933.7.1 Continuous special inspection during all 
field gluing operations of elements of the seismic 
force-resisting system. 



218 



ASCE 7-02 



A B 9.3.3.7.2 Periodic special inspection is required 
for nailing, bolting, anchoring, and other fastening of 
components within the seismic force-resisting system 
including drag struts, braces, and hold-downs. 

A.9.3.3.7.3 Periodic special inspections for nailing 
and other fastening of wood sheathing used for wood 
shear walls, shear panels, and diaphragms where the 
required fastener spacing is 4 in. or less, and which 
are included in the seismic force-resisting system. 

A.9.3.3.8 Cold-Formed Steel Framing. 

A.9.3.3.8.1 Periodic special inspection is required 
during all welding operations of elements of the 
seismic force-resisting system. 

A.9.3.3.8.2 Periodic special inspection is required 
for screw attachment, bolting, anchoring, and other 
fastening of components within the seismic force- 
resisting system including struts, braces, and hold- 
downs. 

A.9.3.3.9 Architectural Components. Special inspec- 
tion for architectural components shall be as follows: 

1 . Periodic special inspection during the erection and 
fastening of exterior cladding, interior and exterior 
nonbearing walls, and interior and exterior veneer 
in Seismic Design Categories D, E, and F. 

Exceptions: 

a. Architectural components less than 30 ft (9 m) 
above grade or walking surface. 

b. Cladding and veneer weighing 5 lb/ft 2 (239 N/ 
m 2 ) or less. 

c. Interior nonbearing walls weighing 15 lbs/ft 2 
(718 N/m 2 ) or less. 

2. Periodic special inspection during the anchor- 
age of access floors, suspended ceilings, and 
storage racks 8 ft (2.5 m) or greater in height 
in Seismic Design Categories D, E, and F. 

3. Periodic special inspection during erection of 
glass 30 ft (9 m) or more above an adjacent 
grade or walking surface in glazed curtain 
walls, glazed storefronts, and interior glazed 
partitions in Seismic Design Categories D. E, 
and F. 

A.9.3.3.10 Mechanical and Electrical Components. 
Special inspection for mechanical and electrical compo- 
nents shall be as follows: 



1. Periodic special inspection during the anchorage 
of electrical equipment for emergency or standby 
power systems in Seismic Design Categories C, D, 

E, and F. 

2. Periodic special inspection during the installation 
of anchorage of all other electrical equipment in 
Seismic Design Categories E and F. 

3. Periodic special inspection during the installation 
for flammable, combustible, or highly toxic piping 
systems and their associated mechanical units in 
Seismic Design Categories C, D, E, and F. 

4. Periodic special inspection during the installation 
of HVAC ductwork that will contain hazardous 
materials in Seismic Design Categories C, D, E, 
and F. 

5. Periodic special inspection during the installation 
of vibration isolation systems when the construc- 
tion documents indicate a maximum clearance (air 
gap) between the equipment support frame and 
restraint less than or equal to 1/4 in. 

A.9.3.3,11 Seismic Isolation System., Periodic special 
inspection is required during the fabrication and instal- 
lation of isolator units and energy-dissipation devices if 
used as part of the seismic isolation system. 

A.9.3.4 Testing. The special inspector(s) shall be respon- 
sible for verifying that the special test requirements are 
performed by an approved testing agency for the types of 
work in designated seismic systems listed below. 

A.9.3.4.1 Reinforcing and Prestressing Steel. Special 
testing of reinforcing and prestressing steel shall be 
as follows: 

A.9.3.4.L1 Examine certified mill test reports for 
each shipment of reinforcing steel used to resist 
flexural and axial forces in reinforced concrete inter- 
mediate and special moment frames and boundary 
members of reinforced concrete shear walls or rein- 
forced masonry shear walls and determine confor- 
mance with construction documents. 

A.9.3.4.1.2 Where ASTM A615 reinforcing steel 
is used to resist earthquake-induced flexural and 
axial forces in special moment frames and in wail 
boundary elements of shear walls in structures of 
Seismic Design Categories D, E, and F, verify that the 
requirements of Section 21.2.5.1 of Ref. 9.9-1 have 
been satisfied. 

A.9.3.4.1.3 Where ASTM A615 reinforcing steel is 
to be welded, verify that chemical, tests have been 



Minimum Design Loads for Buildings and Other Structures 



219 



performed to determine weldabiiity in accordance 
with Section 3.5.2 of Ref. 9.9-1. 

A.9.3.4.2 Structural Concrete. Samples of structural 
concrete shall be obtained at the project site and tested 
in accordance with the requirements of Ref. 9.9-1. 

A.9.3.4.3 Structural Masonry. Quality assurance test- 
ing of structural masonry shall be in accordance with the 
requirements of Ref. 9.11-1. 

A.9.3.4.4 Structural Steel. The testing needed to estab- 
lish that the construction is in conformance with these 
provisions shall be included in a quality assurance plan. 
The minimum testing contained in the quality assurance 
plan shall be as required in Ref. 9.8-3 and the following 
requirements: 

A.9.3.4.4.1 Base Metal Testing, Base metal thicker 
than 1.5 in. (38 mm), when subject to through- 
thickness weld shrinkage strains, shall be ultrason- 
ically tested for discontinuities behind and adjacent 
to such welds after joint completion. Any material 
discontinuities shall be accepted or rejected on the 
basis of ASTM A435, Specification for Straight Beam 
Ultrasound Examination of Steel Plates, or ASTM 
A898. Specification for Straight Beam Ultrasound 
Examination for Rolled Steel Shapes (Level 1 Cri- 
teria), and criteria as established by the registered 
design professional(s) in responsible charge and the 
construction documents. 

A.9.3.4.5 Mechanical and Electrical Equipment. As 
required to ensure compliance with the seismic design 
provisions herein, the registered design professional in 
responsible charge shall clearly state the applicable 
requirements on the construction documents. Each man- 
ufacturer of these designated seismic system components 
shall test or analyze the component and its mounting 
system or anchorage as required and shall submit a cer- 
tificate of compliance for review and acceptance by the 
registered design professional in responsible charge of 
the design of the designated seismic system and for 
approval by the authority having jurisdiction. The basis 
of certification shall be by actual test on a shaking 
table, by three-dimensional shock tests, by an analyti- 
cal method using dynamic characteristics and forces, by 
the use of experience data (i.e., historical data demon- 
strating acceptable seismic performance), or by more 
rigorous analysis providing for equivalent safety. The 
special inspector shall examine the designated seismic 
system and shall determine whether its anchorages and 
label conform with the certificate of compliance. 

A.9.3.4.6 Seismic-Isolated Structures, For required 
system tests, see Section 9.13.9 



A.9.3.5 Structural Observations. Structural observations 
shall be provided for those structures included in Seismic 
Design Categories D, E, and F when one or more of the 
following conditions exist: 

1. The structure is included in Seismic Use Group II or 
Seismic Use Group III, or 

2. The height of the structure is greater than 75 ft above 
the base, or 

3. The structure is in Seismic Design Category E or 
F and Seismic Use Group I and is greater than two 
stories in height. 

Observed deficiencies shall be reported in writing to the 
owner and the authority having jurisdiction. 

A.9.3.6 Reporting and Compliance Procedures. Each 
special inspector shall furnish to the authority having 
jurisdiction, the registered design professional in respon- 
sible charge, the owner, the persons preparing the qual- 
ity assurance plan, and the contractor copies of regular 
weekly progress reports of his observations, noting therein 
any uncorrected deficiencies and corrections of previously 
reported deficiencies. All deficiencies shall be brought to 
the immediate attention of the contractor for correction. 
At completion of construction, each special inspector shall 
submit a final report to the authority having jurisdiction cer- 
tifying that all inspected work was completed substantially 
in accordance with approved construction documents. Work 
not in compliance shall be described in the final report. At 
completion of construction, the building contractor shall 
submit a final report to the authority having jurisdiction 
certifying that all construction work incorporated into the 
seismic force-resisting system and other designated seis- 
mic systems was constructed substantially in accordance 
with the approved construction documents and applicable 
workmanship requirements. Work not in compliance shall 
be described in the final report. The contractor shall correct 
all deficiencies as required. 

SECTION A.9.7 

SUPPLEMENTARY FOUNDATION 

REQUIREMENTS 

A.9.7 A4 Special PISe Requirements for Category C. All 
concrete piles and concrete-filled pipe piles shall be con- 
nected to the pile cap by embedding the pile reinforcement 
in the pile cap for a distance equal to the development 
length as specified in Ref. 9.9-1 as modified by Section 
A9.9 of this Standard or by the use of field-placed dow- 
els anchored in the concrete pile. For deformed bars, the 
development length is the full development length for com- 
pression or tension, in the case of uplift, without reduction 
in length for excess area. 

Hoops, spirals, and ties shall be terminated with seismic 
hooks as defined in Section 21.1 of Ref. 9.9-1. 



220 



ASCE 7-02 



Where required for resistance to uplift forces, anchorage 
of steel pipe (round HSS sections), concrete-filled steel pipe 
or H piles to the pile cap shall be made by means other than 
concrete bond to the bare steel section. 

Exception; Anchorage of concrete-filled steel pipe piles 
is permitted to be accomplished using deformed bars 
developed into the concrete portion of the pile. 

Where a minimum length for reinforcement or the extent 
of closely spaced confinement reinforcement is specified at 
the top of the pile, provisions shall be made so that those 
specified lengths or extents are maintained after pile cutoff. 

A.9.7.4.4.1 Uncased Concrete Piles. Reinforcement 
shall be provided where required by analysis. As a 
minimum, longitudinal reinforcement ratio of 0.0025 
shall be provided for uncased cast-in-place concrete 
drilled or augered piles, piers, or caissons in the top 
one-third of the pile length or a minimum length of 
10 ft (3 m) below the ground. There shall be a min- 
imum of four longitudinal bars with closed ties (or 
equivalent spirals) of a minimum of a 3/8 in. (9 mm) 
diameter provided at 16 longitudinal-bar-diameter 
maximum spacing. Transverse confinement reinforc- 
ing with a maximum spacing of 6 in. (152 mm) or 
8 longitudinal-bar-diameters, whichever is less, shall 
be provided in the pile within three pile diameters of 
the bottom of the pile cap. 

A.9.7.4A2 Metal-Cased Concrete Piles. Reinforce- 
ment requirements are the same as for uncased con- 
crete piles. 

Exception: Spiral welded metal casing of a thick- 
ness not less than No. 14 gauge can be considered 
as providing concrete confinement equivalent to 
the closed ties or equivalent spirals required in an 
uncased concrete pile, provided that the metal cas- 
ing is adequately protected against possible dele- 
terious action due to soil constituents, changing 
water levels, or other factors indicated by boring 
records of site conditions. 

A.9.7.4A3 Concrete-Filled Pipe. Minimum rein- 
forcement 0.01 times the cross-sectional area of the 
pile concrete shall be provided in the top of the pile 
with a length equal to two times the required cap 
embedment anchorage into the pile cap. 

A.9.7.4.4.4 Precast Nonprestressed Concrete Piles. 
A minimum longitudinal steel reinforcement ratio 
of 0.01 shall be provided for precast nonprestressed 
concrete piles. The longitudinal reinforcing shall be 
confined with closed ties or equivalent spirals of a 
minimum 3/8 in. (10 mm) diameter. Transverse con- 
finement reinforcing shall be provided at a maximum 



spacing of eight times the diameter of the smallest 
longitudinal bar, but not to exceed 6 in. (152 mm), 
within three pile diameters of the bottom of the 
pile cap. Outside of the confinement region, closed 
ties or equivalent spirals shall be provided at a 16 
longitudinal-bar-diameter maximum spacing, but not 
greater than 8 in. (200 mm). Reinforcement shall be 
full length. 

A.9.7.4.4.5 Precast Prestressed Piles. For the upper 
20 ft (6 m) of precast prestressed piles, the minimum 
volumetric ratio of spiral reinforcement shall not 
be less than 0.007 or the amount required by the 
following formula: 



0.12/, 

fyh 



(Eq. A.9.7.4.4.5-1) 



where 



p s = volumetric ratio (vol. spiral/vol. core) 

f c — specified compressive strength of concrete, 

psi (MPa) 
fyh — specified yield strength of spiral 

reinforcement, which shall not be taken 
greater than 85,000 psi (586 MPa) 

A minimum of one-half of the volumetric ratio 
of spiral reinforcement required by Eq. A.9.7.4.4.5-1 
shall be provided for the remaining length of the pile. 

A.9.7.5 Special Pile Requirements for Categories D, E, 
and F. 

A.9.7.5.4.1 Uncased Concrete Piles, A minimum 
longitudinal reinforcement ratio of 0.005 shall be pro- 
vided for uncased cast-in-place drilled or augered 
concrete piles, piers, or caissons in the top one-half 
of the pile length, or a minimum length of 10 ft 
(3m) below ground, or throughout the flexural length 
of the pile, whichever length is greatest. The flexu- 
ral length shall be taken as the length of pile to a 
point where the concrete section cracking moment 
multiplied by the resistance factor 0.4 exceeds the 
required factored moment at that point. There shall 
be a minimum of four longitudinal bars with trans- 
verse confinement reinforcement in the pile in accor- 
dance with Sections 21.4.4.1, 21.4.4.2, and 21 A A3 
of Ref. 9.9-1. Such transverse confinement reinforce- 
ment shall extend the full length of the pile in Site 
Classes E or F, a minimum of seven times the least 
pile dimension above and below the interfaces of soft 
to medium stiff clay or liquefiable strata, and three 
times the least pile dimension below the bottom of 
the pile cap in Site Classes other than E or F. 

In other than Site Classes E or F, it shall be 
permitted to use a transverse spiral reinforcement 



Minimum Design Loads for Buildings and Other Structures 



221 



ratio of not less than one-half of that required 
in Section 21.4.4.1(a) of Ref. 9.9-1 throughout the 
remainder of the pile length. Tie spacing through- 
out the remainder of the pile length shall not. exceed 
12 longitudinal-bar-diameters, one-half the diame- 
ter of the section, or 12 in. (305 mm). Ties shall 
be a minimum of No. 3 bars for up to 20-in.- 
diameter (500 mm) piles and No. 4 bars for piles of 
larger diameter. 

A.9.7.5.4.2 Metal-Cased Concrete Files. Reinforce- 
ment requirements are the same as for uncased con- 
crete piles. 

Exception: Spiral welded metal-casing of a thick- 
ness not less than No. 14 gauge can be considered 
as providing concrete confinement equivalent to 
the closed ties or equivalent spirals required in an 
uncased concrete pile, provided that the metal cas- 
ing is adequately protected against possible dele- 
terious action doe to soil constituents, changing 
water levels, or other factors indicated by boring 
records of site conditions. 

A.9.7.5.4.3 Precast Concrete Piles. Transverse con- 
finement reinforcement consisting of closed ties or 
equivalent spirals shall be provided in accordance 
with Sections 21.4.4.1, 21.4.4.2, and 21.4.4.3 of 
Ref. 9.9-1 for the full length of the pile. 

Exception: In other than Site Classes E or F, 
the specified transverse confinement reinforcement 
shall be provided within three pile diameters below 
the bottom of the pile cap, but it shall be permitted 
to use a transverse reinforcing ratio of not less than 
one-half of that required in Section 21.4.4.1(a) 
of Ref. 9,9-1 throughout the remainder of the 
pile length. 

A.9.7,5.4.4 Precast Prestressed Piles. In addition to 
the requirements for Seismic Design Category C, the 
following requirements shall be met: 

1. Requirements of Ref. 9.9-1, Chapter 21, need 
not apply. 

2. Where the total pile length in the soil is 
35 ft (10,668 mm) or less, the lateral transverse 
reinforcement in the ductile region shall occur 
through the length of the pile. Where the pile 
length exceeds 35 ft (10,668 mm), the ductile 
pile region shall be taken as the greater of 35 ft 
(10,668 mm) or the distance from the underside 
of the pile cap to the point of zero curvature plus 
three times the least pile dimension. 

3. In the ductile region, the center-to-center spac- 
ing of the spirals or hoop reinforcement shall 



not exceed one-fifth of the least pile dimension, 
six times the diameter of the longitudinal strand, 
or 8 in. (203 mm), whichever is smaller. 

4. Spiral reinforcement shall be spliced by lap- 
ping one full turn by welding or by the use 
of a mechanical connector. Where spiral rein- 
forcement is lap spliced, the ends of the spiral 
shall terminate in a seismic hook in accor- 
dance with Ref. 9.9-1, except that the bend shall 
be not less than 135 degrees. Welded splices 
and mechanical connectors shall comply with 
Section 12.14.3 of Ref. 9.9-1. 

5. Where the transverse reinforcement consists of 
circular spirals, the volumetric ratio of spiral 
transverse reinforcement in the ductile region 
shall comply with: 



p s = 0.25 



fc 



fyh 
0.5 4 



^-1.0 



1.4P 



fc^ g 



but not less than 



p s -0.12 



A. 

fyh 



0.5 + 



\AP 



f^ g 



and not to exceed p s = 0.021 
where 

p s = volumetric ratio (vol. spiral/vol. core) 
/; < 6000 psi (41.4 MPa) 
fyh = yield strength of spiral reinforcement 

<85 ksi (586 MPa) 
A g = pile cross-sectional area, in. 2 (mm 2 ) 
A c h ~ core area defined by spiral outside 

diameter, in. 2 (mm 2 ) 
P = axial load on pile resulting from the 

load combination 1 2D + 0.5L 4- 1.0£, 

pounds (kN) 

This required amount of spiral reinforcement is 
permitted to be obtained by providing an inner 
and outer spiral. 

6. When transverse reinforcement consists of rect- 
angular hoops and cross ties, the total cross- 
sectional area of lateral transverse reinforcement 
in the ductile region with spacings, and perpen- 
dicular to dimension, h C7 shall conform to: 



A sh = 03sh c 



fc 



fyh 
0.5 + 



A c h 
IAP~ 



1.0 



222 



ASCE 7-02 



but not less than 



A sh =0.\2sh c 



fyh 



0.5 + 



\AP 



where 



s = spacing of transverse reinforcement 
measured along length of pile, in (mm) 
h c — cross- sectional dimension of pile core 
measured center-to-center of hoop 
reinforcement, in (mm) 
fyh < 70 ksi (483 MPa) 

The hoops and cross ties shall be equivalent 
to deformed bars not less than No. 3 in size. 
Rectangular hoop ends shall terminate at a 
corner with seismic hooks. 

Outside of the length of the pile requiring trans- 
verse reinforcement, the spiral or hoop reinforcement 
with a volumetric ratio not less than one-half of 
that required for transverse confinement reinforce- 
ment shall be provided. 

A.9.7.5.4.5 Steel Piles. The connection between the 
pile cap and steel piles or unfilled steel pipe piles 
shall be designed for a tensile force equal to 10% of 
the pile compression capacity. 

Exceptions: Connection tensile capacity need not 
exceed the strength required to resist the special 
seismic loads of Section 9.5.2.7.1. Connections 
need not be provided where the foundation or 
supported structure does not rely on the tensile 
capacity of the piles for stability under the design 
seismic forces. 

SECTION A.9.8 
SUPPLEMENTARY PROVISIONS FOR STEEL 

A.9.8.1 General. The design, construction, and quality of 
steel components that resist seismic forces shall conform 
to the requirements of the references listed in Section 9.8 
except as modified by the requirements of this section. 

A.9.8.2 Seismic Requirements for Steel Structures. 
Steel structures and structural elements therein that resist 
seismic forces shall be designed in accordance with the 
requirements of Sections A. 9. 8. 3 and A.9.8.4 for the 
appropriate Seismic Design Category. 

A.9.8.3 Seismic Design Categories A, B 9 and C Steel 
structures assigned to Seismic Design Categories A, B, and 
C shall be of any construction permitted by the references in 
Section A.9.8.1. 1. An R factor as set forth in Table 9.5.2.2 
shall be permitted when the structure is designed and 
detailed in accordance with the requirements of Ref. 9.8-3 



for structural steel buildings as modified by this chapter 
and Section A.9.8.7 for light-framed walls. Systems not 
detailed in accordance with Ref. 9.8-3 shall use the R factor 
designated for ''Systems not detailed for seismic." 

A.9.8.4 Seismic Design Categories D, E, and F. Steel 
structures assigned to Seismic Design Categories D, E, 
and F shall be designed and detailed in accordance with 
Ref. 9.8-3 Part I or Part III or Section A.9.8.6 for light- 
framed cold-formed steel wall systems. 

A.9.8.5 Cold-Formed Steel Seismic Requirements. The 
design of cold-formed carbon or low-alloy steel to resist 
seismic loads shall be in accordance with the provisions 
of Ref. 9.8-4, and the design of cold-formed stainless 
steel structural members to resist seismic loads shall be 
in accordance with the provisions of Ref. 9.8-5, except 
as modified by this section. The references to section 
and paragraph numbers are to those of the particular 
specification modified. 

A.9.8.5.1 Revise Section A5. 1.3 of Ref. 9.8-4 by 
deleting the reference to earthquake or seismic loads 
in the sentence permitting the 0.75 factor. Seismic load 
combinations shall be as determined by ASCE 7. 

A.9.8.6 Light-Framed Wall Requirements, Cold-formed 
steel stud wall systems designed in accordance with 
Ref. 9.8-4 or 9.8-5 shall, when required by the provisions of 
Sections A.9.8.3 or A.9.8.4, also comply with the require- 
ments of this section. 

A.9.8.6.1 Boundary Members. All boundary mem- 
bers, chords, and collectors shall be designed to trans- 
mit the axial force induced by the specified loads of 
Section 9. 

A.9.8.6.2 Connections. Connections of diagonal brac- 
ing members, top chord splices, boundary members, and 
collectors shall have a design strength equal to or greater 
than the nominal tensile strength of the members being 
connected or Q G times the design seismic forces. The 
pullout resistance of screws shall not be used to resist 
seismic forces. 

A.9.8.6.3 Braced Bay Members. In stud systems where 
the lateral forces are resisted by braced frames, the 
vertical and diagonal members of braced bays shall be 
anchored such that the bottom tracks are not required to 
resist tensile forces by bending of the track or track web. 
Both flanges of studs in a bracing bay shall be braced to 
prevent lateral torsional buckling. In braced shear walls, 
the vertical boundary members shall be anchored so the 
bottom track is not required to resist uplift forces by 
bending of the track web. 



Minimum Design Loads for Buildings and Other Structures 



223 



A.9.8.6.4 Diagonal Braces. Provision shall be made 
for pre-tensioning or other methods of installation of 
tension-only bracing to prevent loose diagonal straps. 

A.9.8.6.5 Shear Walls. Nominal shear values for wall 
sheathing materials are given in Table A.9.8.6.5. Design 
shear values shall be determined by multiplying the 
nominal values therein by a factor of 0.55. In structures 
over 1 story in height, the assemblies in Table A.9.8.6.5 
shall not be used to resist horizontal loads contributed 
by forces imposed by masonry or concrete construction. 

Panel thicknesses shown in Table A.9.8.6.5 shall be 
considered to be minimums. No panels less than 2-in. 
wide shall be used. Plywood or oriented strand board 
structural panels shall be of a type that is manufactured 
using exterior glue. Framing members, blocking, or 
strapping shall be provided at the edges of all sheets. 
Fasteners along the edges in shear panels shall be placed 
not less than 3/8 in. (9.5 mm) in from panel edges. 
Screws shall be of sufficient length to ensure penetration 
into the steel stud by at least two full diameter threads. 

The height-to-length ratio of wall systems listed in 
Table A.9.8.6.5 shall not exceed 2:1. 

Perimeter members at openings shall be provided and 
shall be detailed to distribute the shearing stresses. Wood 
sheathing shall not be used to splice these members. 

Wall studs and track shall have a minimum uncoated 
base thickness of not less than 0.033 in. (0.84 mm) and 
shall not have an uncoated base metal thickness greater 
than 0.048 in. (1.22 mm). Panel end studs and their 
uplift anchorage shall have the design strength to resist 
the forces determined by the seismic loads determined 
by Eqs. 9.5.2.7.1-1 and 9.5.2.7.1-2. 

A.9.8.7 Seismic Requirements for Steel Deck Dia- 
phragms. Steel deck diaphragms shall be made from mate- 
rials conforming to the requirements of Ref. 9.8-4 or 9.8-5. 
Nominal strengths shall be determined in accordance with 
approved analytical procedures or with test procedures pre- 
pared by a registered design professional experienced in 
testing of cold-formed steel assemblies and approved by 
the authority having jurisdiction. Design strengths shall be 
determined by multiplying the nominal strength by a resis- 
tance factor, <p equal to 0.60 for mechanically connected 
diaphragms and equal to 0.50 for welded diaphragms. The 
steel deck installation for the building, including fasteners, 
shall comply with the test assembly arrangement. Quality 
standards established for the nominal strength test shall be 
the minimum standards required for the steel deck installa- 
tion, including fasteners. 

A.9.8.8 Steel Cables. The design strength of steel cables 
shall be determined by the provisions of Ref. 9,8-7 except 
as modified by this section. Ref. 9.8-7, Section 5d, shall be 
modified by substituting 1.5(T 4 ) when T 4 is the net tension 
in cable due to dead load, prestress, live load, and seismic 



load. A load factor of 1.1 shall be applied to the prestress 
force to be added to the load combination of Section 3.1.2 
of Ref. 9.5-7. 



SECTION A.9.9 

SUPPLEMENTAL PROVISIONS FOR 

CONCRETE 

A.9.9.1 Modifications to Ref. 9.9-1 (ACI 318-02). The 
text of Ref. 9.9-1 (ACI 318-02) shall be modified as 
indicated in Sections A.9.9.1.1 through A. 9.9. 1.6. Italic type 
is used for text within Sections A.9.9.1.1 through A. 9. 9. 1.6 
to indicate provisions which differ from Ref. 9.9-1 (ACI 
318-02). 

A.9.9.1.1 ACI 318, Section 21.0. Add the following 
notations to Section 21.0: 

h — overall dimension of member in the direction of 
action considered 

A.9.9.1.2 ACI 318, Section 21.1. Add the following 
definition to Section 21.1. 



Wall Pier. A wall segment with a horizontal length- 
to-thickness ratio of at least 2.5, but not exceeding 6, 
whose clear height is at least two times its horizontal 
length 

A.9.9.1.3 ACI 318, Section 21.2.5. Modify Section 
21.2.5 by renumbering as Section 21.2.5.1 and adding 
new Sections 21.2.5.2, 21.2.5.3, and 21.2.5.4 to read 
as follows: 

21.2.5 Reinforcement in Members Resisting 
Earthquake-Induced Forces. 

21.2.5.1 Except as permitted in Sections 21,2.5.2 and 
21.2.53, reinforcement resisting earthquake-induced flex- 
ural and axial forces in frame members and in wall bound- 
ary elements shall comply with ASTM A706. ASTM 
A615 Grades 40 and 60 reinforcement shall be permitted 
in these members if (a) the actual yield strength based on 
mill tests does not exceed the specified yield strength by 
more than 18,000 psi (retests shall not exceed this value 
by more than an additional 3000 psi), and (b) the ratio 
of the actual ultimate tensile strength to the actual tensile 
yield strength is not less than 1.25. 

21.2.5.2 Prestressing tendons shall be permitted in flex- 
ural members of frames provided the average prestress, 
f P c, calculated for an area equal to the member's 
shortest cross-sectional dimension multiplied by the per- 
pendicular dimension shall be the lesser of 700 psi 



224 



ASCE 7-02 



(4.83 MP a) or f ! c /6 at locations of nonlinear action 
where prestressing tendons are used in members of 
frames. 



2L7.163 Wall segments with a horizontal length-to- 
thickness ratio less than 2 1/2, shall be designed as 
columns. 



21.2,5.3 Unless the seismic force-resisting frame is qual- 
ified for use through structural testing as required by 
the ACI Provisional Standard AC I 71.1-01, Acceptance 
Criteria for Moment Frames Based on Structural 7est- 
ing, for members in which prestressing tendons are used, 
together with mild reinforcement to resist earthquake- 
induced forces, prestressing tendons shall not provide 
more than one-quarter of the strength for either posi- 
tive or negative moments at the nonlinear action location 
and shall be anchored at the exterior face of the joint 
or beyond. 



A.9.9.1.5 ACI 318, Section 21.10. Modify 
21.10.1.1 to read as follows: 



Section 



21,8.1 Foundations resisting earthquake-induced forces 
or transferring earthquake-induced forces between struc- 
ture and ground shall comply with requirements of 
Section 21.10 and other applicable code provisions unless 
modified by Section 9.7 of ASCE 7-02. 

A.9.9.1.6 ACI 318, Section 21.11. Modify Section 
21.11.2.2 to read as follows: 



21,2.5.4 Anchorages for tendons shall be demonstrated 
to perform satisfactorily for seismic loadings. Anchorage 
assemblies shall withstand, without failure, a minimum of 
50 cycles of loading ranging between 40% and 85% of 
the minimum specified tensile strength of the prestress- 
ing steel 

A.9.9.1.4 ACI 318, Section 21.7. Modify Sec- 
tion 21.7 by adding a new Section 21.7.10 to read 
as follows: 

21.7.10 Wall Piers and Wall Segments. 

21.7.10.1 Wall piers not designed as a part of a spe- 
cial moment-resisting frame shall have transverse rein- 
forcement designed to satisfy the requirements in Sec- 
tion 21.7.10.2. 



21.11.2.2 Members with factored gravity axial forces 
exceeding (A g f' c /10) shall satisfy Sections 21.4.3.1, 
21.4.4.1 (c), 21.4.4.3, and 21.4.5. The maximum lon- 
gitudinal spacing of ties shall be s for the full column 
height. The spacing s shall not be more than six diam- 
eters of the smallest longitudinal bar enclosed or 6 in. 
(152 mm), whichever is smaller. 



A.9.9.1.7 ACI 318 Section D.4.2. Modify Appendix 
Section D.4 by adding a new Exception at the end of 
Section D.4.2. 2 to read as follows: 

Exception: If 7V/ ? is determined using Eq. D-6a, the 
concrete breakout strength of D.4.2 shall be consid- 
ered satisfied by the design procedure of D.5.2 and 
D.6.2 without the need for testing regardless of anchor 
bolt diameter and tensile embedment. 



Exceptions: 

1. Wall piers that satisfy Section 21.11. 

2. Wall piers along a wall line within a story 
where other shear wall segments provide lateral 
support to the wall piers, and such segments 
have a total stiffness of at least six times the 
sum of the stiffnesses of all the wall piers. 



A.9.9.2 Classification of Shear Walls. Structural concrete 
shear walls which resist seismic forces shall be classified 
in accordance with Sections A.9.9.2. 1 through A.9.9.2. 4. 



A.9.9.2. 1. Ordinary Plain Concrete Shear Walls. 
Ordinary plain concrete shear walls are walls conforming 
to the requirements of Ref . 9.9-1 for ordinary structural 
plain concrete walls. 



21.7.10.2 Transverse reinforcement shall be designed to 
resist the shear forces determined from Sections 21,4.5.1 
and 21.3.4.2. Where the axial compressive force, includ- 
ing earthquake effects, is less than A^/ c 720, trans- 
verse reinforcement in wall piers is permitted to have 
standard hooks at each end in lieu of hoops. Spac- 
ing of transverse reinforcement shall not exceed 6 in. 
(152 mm). Transverse reinforcement shall be extended 
beyond the pier clear height for at least the development 
length of the largest longitudinal reinforcement in the 
wall pier. 



A.9.9.2.2 Detailed Plain Concrete Shear Walls. 
Detailed plain concrete shear walls are walls conform- 
ing to the requirements for ordinary plain concrete shear 
walls and shall have reinforcement as follows. Verti- 
cal reinforcement of at least 0.20 in. 2 (129 mm 2 ) in 
cross-sectional area shall be provided continuously from 
support to support at each corner, at each side of each 
opening, and at the ends of walls. The continuous ver- 
tical bar required beside an opening is permitted to 
substitute for one of the two No. 5 bars required by 
Section 22.6.6.5 of Ref. 9.9-1. Horizontal reinforcement 



Minimum Design Loads for Buildings and Other Structures 



225 



at least 0.20 in. 2 (129 mm 2 ) in cross-sectional area shall 
be provided: 

1. Continuously at structurally connected roof and 
floor levels and at the top of walls. 

2. At the bottom of load-bearing walls or in the top 
of foundations where doweled to the wall. 

3. At a maximum spacing of 120 in. (3048 mm). 

Reinforcement at the top and bottom of openings, 
where used in determining the maximum spacing speci- 
fied in Item. 3 above, shall be continuous in the wall. 

A.9.9.2.3 Ordinary Reinforced Concrete Shear 
Walls. Ordinary reinforced concrete shear walls are 
walls conforming to the requirements of Ref. 9.9-1 for 
ordinary reinforced concrete structural walls. 

A.9.9.2.4 Special Reinforced Concrete Shear Walls. 
Special reinforced concrete shear walls are walls con- 
forming to the requirements of Ref. 9.9-1 for special 
reinforced concrete structural walls or special precast 
structural walls. 

A.9.9.3 Seismic Design Category B. Structures assigned 
to Seismic Design Category B, as determined in Section 
9.4.2, shall conform to the requirements for Seismic Design 
Category A and to the additional requirements for Seismic 
Design Category B of this section, 

A.9.9.3.1 Ordinary Moment Frames. In flexural mem- 
bers of ordinary moment frames forming part of the 
seismic force-resisting system, at least two main flexu- 
ral reinforcing bars shall be provided continuously top 
and bottom throughout the beams, through or developed 
within exterior columns or boundary elements. 

Columns of ordinary moment frames having a clear 
height to maximum plan dimension ratio of five or 
less shall be designed for shear in accordance with 
Section 21.12.3 of Ref. 9.9-1. 

A.9.9.4 Seismic Design Category C« Structures assigned 
to Seismic Design Category C, as determined in Section 
9.4.2, shall conform to the requirements for Seismic Design 
Category B and to the additional requirements for Seismic 
Design Category C of this section. 

A.9.9.4.1 Seismic Force-Resisting Systems, Moment 
frames used to resist seismic forces shall be 
"intermediate moment frames" or "special moment 
frames." Shear walls used to resist seismic forces 
shall be ordinary reinforced concrete shear walls, 
or special reinforced concrete shear walls. Ordinary 
reinforced concrete shear walls constructed of precast 



concrete elements shall comply with the additional 
requirements of Section 21.13 of Ref. 9.9-1 (ACI 318) 
for intermediate precast concrete structural walls. 

A.9.9.4.2 Discontinuous Members. Columns support- 
ing reactions from discontinuous stiff members such 
as walls shall be designed for the special load combi- 
nations in Section 9.5.2.7 and shall be provided with 
transverse reinforcement at the spacing s as defined 
in Section 21.12.5.1 of Ref. 9.9-1 over their full height 
beneath the level at which the discontinuity occurs. This 
transverse reinforcement shall be extended above and 
below the column as required in Section 21.4.4.5 of 
Ref. 9.9-1. 

A.9.9.4.3 Anchor Bolts in the Top of Columns. An- 
chor bolts set in the top of a column shall be provided 
with ties that enclose at least four longitudinal column 
bars. There shall be at least two No. 4, or three No. 3 ties 
within 5 in. of the top of the column. The ties shall have 
hooks on each free end that comply with Section 7.1.3(c) 
of Ref. 9.9-1. 

A.9.9A4 Plain Concrete. Structural plain concrete 
members in structures assigned to Seismic Design Cat- 
egory C shall conform to Ref. 9.9-1 and Sections 
A.9.9.4.4.1 through A.9.9.4.4.3. 

A.9.9.4.4.1 Walls. Structural plain concrete walls are 
not permitted in structures assigned to Seismic Design 
Category C. 

Exception: Structural plain concrete basement, 
foundation, or other walls below the base are per- 
mitted in detached one-and two-family dwellings 
constructed with stud-bearing walls. Such walls 
shall have reinforcement in accordance with Section 
22.6.6.5 of Ref. 9.9-1. 

A.9.9.4.4.2 Footings. Isolated footings of plain con- 
crete supporting pedestals or columns are permitted 
provided the projection of the footing beyond the face 
of the supported member does not exceed the foot- 
ing thickness. 

Exception: In detached one- and two-family 
dwellings, three stories or less in height, the pro- 
jection of the footing beyond the face of the sup- 
ported member is permitted to exceed the footing 
thickness. 

Plain concrete footings supporting walls shall be 
provided with not less than two continuous longitu- 
dinal reinforcing bars. Bars shall not be smaller than 
No. 4 and shall have a total area of not less than 0.002 



226 



ASCE 7-02 



times the gross cross-sectional area of the footing. For 
footings that exceed 8 in. (203 mm) in thickness, a 
minimum of one bar shall be provided at the top and 
bottom of the footing. For foundation systems consist- 
ing of a plain concrete footing and a plain concrete 
stem wall, a minimum of one bar shall be provided at 
the top of the stemwall and at the bottom of the foot- 
ing. Continuity of reinforcement shall be provided at 
corners and intersections. 

Exceptions; 

1. In detached one- and two-family dwellings, 
three stories or less in height and con- 
structed with stud-bearing walls, plain con- 
crete footings supporting walls are permitted 
without longitudinal reinforcement. 

2. Where a slab-on-ground is cast monolith- 
ically with the footing, one No. 5 bar is 
permitted to be located at either the top or 
bottom of the footing. 

A.9.9.4.4.3 Pedestals, Plain concrete pedestals shall 
not be used to resist lateral seismic forces. 

A.9.9.5 Seismic Design Categories D, E, and F. Struc- 
tures assigned to Seismic Design Categories D, E, or 
F, as determined in Section 9.4.2, shall conform to the 
requirements for Seismic Design Category C and to the 
additional requirements of this section. 

A.9.9.5.1 Seismic Force-Resisting Systems. Moment 
frames used to resist seismic forces shall be special 
moment frames. Shear walls used to resist seismic forces 
shall be special reinforced concrete shear walls. 

A.9.9.5,2 Frame Members Not Proportioned to Resist 
Forces Induced by Earthquake Motions. Frame com- 
ponents assumed not to contribute to lateral force resis- 
tance shall conform to Section 21.11 of Ref. 9.9-1. 



SECTION A.9.11 

SUPPLEMENTARY PROVISIONS FOR 
MASONRY 

A.9.11, 1 For the purposes of design of masonry structures 
using the earthquake loads given in ASCE 7, several 
amendments to the reference standard are necessary. 

A.9.11.2 The references to "Seismic Performance Cat- 
egory" in Section 1.13 and elsewhere of the reference 
standard shall be replaced by "Seismic Design Cate- 
gory," and the rules given for Category E also apply to 
Category F. 



A.9.11.3 The anchorage forces given in Section 1.13.3.2 
of the reference standard shall not be interpreted to 
replace the anchorage forces given in Section 9 of this 
standard. 

A.9.11.4 To qualify for the R factors given in Section 9 
of this standard, the requirements of the reference standard 
shall be satisfied and amended as follows: 

Ordinary and detailed plain masonry shear walls shall be 
designed according to Sections 2.1 and 2.2 of the reference 
standard. Detailed plain masonry shear walls shall be 
reinforced as a minimum as required in Section 1.13.5.3.3 
of the reference standard. 

Ordinary, intermediate, and special reinforced masonry 
shear walls shall be designed according to Sections 2.1 and 
2.3 of the reference standard. Ordinary and intermediate 
reinforced masonry shear walls shall be reinforced as a 
minimum as required in Section 1.13.5.3.3 of the reference 
standard. In addition, intermediate reinforced masonry 
shear walls shall have vertical reinforcing bars spaced no 
farther apart than 48 in. Special reinforced masonry shear 
walls shall be reinforced as a minimum as required in 
Sections 1.13.6.3 and 1.13.6.4 of the reference standard. 

Special reinforced masonry shear walls shall not have a 
ratio of reinforcement, p, that exceeds that given by either 
Method A or B below: 

A.9.11.4.1 Method A. Method A is permitted to be 
used where the story drift does not exceed 0.010/z^ 
as given in Table 9.5.2.8 and if the extreme compres- 
sive fiber strains are less than 0.0035 in./in. (mm/mm) 
for clay masonry and 0.0025 in./in./ (mm/mm) for con- 
crete masonry. 

1. When walls are subjected to in-plane forces, and 
for columns and beams, the critical strain condition 
corresponds to a strain in the extreme tension rein- 
forcement equal to five times the strain associated 
with the reinforcement yield stress, f y . 

2. When walls are subjected to out-of-plane forces, 
the critical strain condition corresponds to a strain 
in the reinforcement equal to 1.3 times the strain 
associated with reinforcement yield stress, f y . 

The strain at the extreme compression fiber shall be 
assumed to be 0.0035 in./in. (mm/mm) for clay masonry 
and 0.0025 in./in. (mm/mm) for concrete masonry. 

The calculation of the maximum reinforcement ratio 
shall include factored gravity axial loads. The stress in 
the tension reinforcement shall be assumed to be 1.25 f y . 
Tension in the masonry shall be neglected. The strength 
of the compressive zone shall be calculated as 80% of 
the area of the compressive zone. Stress in reinforcement 
in the compression zones shall be based on a linear strain 
distribution. 



Minimum Design Loads for Buildings and Other Structures 



227 



A.9.11.4.2 Method B. Method B is permitted to be 
used where story drift does not exceed 0.01 3h sx as given 
in Table 9.5.2.8. 

1 . Boundary members shall be provided at the bound- 
aries of shear walls when the compressive strains 
in the wall exceed 0.002. The strain shall be deter- 
mined using factored forces and R equal to 1.5. 

2. The minimum length of the boundary member 
shall be three times the thickness of the wall, 
but shall include all areas where the compressive 
strain per Section A.9.11.4.2 item 1, is greater 
than 0.002. 

3. Lateral reinforcement shall be provided for the 
boundary elements. The lateral reinforcement shall 



be a minimum of No. 3 closed ties at a maximum 
spacing of 8 in. (203 mm) on center within the 
grouted core, or equivalent approved confinement, 
to develop an ultimate compressive strain of at 
least 0.006. 

4. The maximum longitudinal reinforcement ratio 
shall not exceed 0A5f^/f v . 

A.9.11.5 Where allowable stress design is used for load 
combinations including earthquake, load combinations 3 
and 5 of Section 2.4.1 of this standard shall replace com- 
binations (c) and (e) of Section 2.1.1.1.1 of the reference 
standard. If the increase in stress given in 2.1.1.1.3 of the 
reference standard is used, the restriction on load reduction 
in Section 2.4.3 of this standard shall be observed. 



TABLE A.9.8.6.5 

NOMINAL SHEAR VALUES FOR SEISMIC FORCES FOR SHEAR WALLS FRAMED WITH 

COLD-FORMED STEEL STUDS (IN LBS/FT) ab 



Assembly 
Description 


Fastener Spacing at 

Panel Edges 

(in.) 


Framing 
Spacing 
(in. o.c.) 


6 


4 


3 


2 


15/32 in. rated structural I sheathing 
(4-ply) plywood one side d 


780 


990 


1465 


1625 


24 


7/16 in. oriented strand board one 

side d 


700 


915 


1275 


1625 


24 



Note: For fastener and framing spacing, multiply inches by 25.4 to obtain mm. 

a Nominal shear values shall be multiplied by the appropriate strength reduction factor to determine design strength 

as set forth in Section A.9.8.6.5. 

b Studs shall be a minimum 1 5/8 in. x 3 1/2 in. with a 3/8 in. return lip. Track shall be a minimum 11/4 in. x 

3 1/2 in. Both studs and track shall have a minimum uncoated base metal thickness of 0.033 in. and shall be 

ASTM A653 SS Grade 33, ASTM A792 SS Grade 33, or ASTM A875 SS Grade 33. Framing screws shall be No. 

8x5/8 in. wafer head self-drilling. Plywood and OSB screws shall be a minimum No. 8x1 in. bugle head. Where 

horizontal straps are used to provide blocking, they shall be a minimum 1 1/2 in. wide and of the same material 

and thickness as the stud and track. 

c Screws in the field of the panel shall be installed 12 in. on center unless otherwise shown. 

d Both flanges of the studs shall be braced in accordance with Section A.9.8.6.3. 



228 



ASCE 7-02 



APPENDIX B.O 

SERVICEABILITY CONSIDERATIONS 



This Appendix is not a mandatory part of the standard, 
but provides guidance for design for serviceability in order 
to maintain the function of a building and the comfort of its 
occupants during normal usage. Serviceability limits (e.g.. 
maximum static deformations, accelerations, and so on) 
shall be chosen with due regard to the intended function 
of the structure. 

Serviceability shall be checked using appropriate loads 
for the limit state being considered. 



SECTION B.1 
DEFLECTION, VIBRATION, AND DRIFT 

B.l.l Vertical Deflections. Deformations of floor and roof 
members and systems due to service loads shall not impair 
the serviceability of the structure. 

B.1.2 Drift of Walls and Frames. Lateral deflection or 
drift of structures and deformation of horizontal diaphragms 
and bracing systems due to wind effects shall not impair 
the serviceability of the structure. 

B.1.3 Vibrations. Floor systems supporting large open 
areas free of partitions or other sources of damping, where 
vibration due to pedestrian traffic might be objectionable, 
shall be designed with due regard for such vibration. 

Mechanical equipment that can produce objectionable 
vibrations in any portion of an inhabited structure shall be 
isolated to minimize the transmission of such vibrations to 
the structure. 

Building structural systems shall be designed so that 
wind-induced vibrations do not cause occupant discomfort 
or damage to the building, its appurtenances, or its contents. 



SECTION B.2 
DESIGN FOR LONG-TERM DEFLECTION 

Where required for acceptable building performance, mem- 
bers and systems shall be designed to accommodate long- 
term irreversible deflections under sustained load. 



SECTION B.3 
CAMBER 

Special camber requirements that are necessary to bring a 
loaded member into proper relations with the work of other 
trades shall be set forth in the design documents. 

Beams detailed without specified camber shall be posi- 
tioned during erection so that any minor camber is upward. 
If camber involves the erection of any member under 
preload, this shall be noted in the design documents. 



SECTION B.4 
EXPANSION AND CONTRACTION 

Dimensional changes in a structure and its elements due to 
variations in temperature, relative humidity, or other effects 
shall not impair the serviceability of the structure. 

Provision shall be made either to control crack widths 
or to limit cracking by providing relief joints. 



SECTION B.5 
DURABILITY 

Buildings and other structures shall be designed to toler- 
ate long-term environmental effects or shall be protected 
against such effects. 



Minimum Design Loads for Buildings and Other Structures 



229 



COMMENTARY TO AMERICAN SOCIETY OF CIVIL 
ENGINEERS STANDARD 7-02 



(This Commentary is not a part of the ASCE Standard 
Minimum Design Loads for Buildings and Other Structures, 
It is included for information purposes.) 

This Commentary consists of explanatory and supple- 
mentary material designed to assist local building code 
committees and regulatory authorities in applying the rec- 
ommended requirements. In some cases, it will be necessary 
to adjust specific values in the standard to local conditions; 
in others, a considerable amount of detailed information 
is needed to put the provisions into effect. This Commen- 



tary provides a place for supplying material that can be 
used in these situations and is intended to create a better 
understanding of the recommended requirements through 
brief explanations of the reasoning employed in arriving 
at them. 

The sections of the Commentary are numbered to 
correspond to the sections of the standard to which they 
refer. Since it is not necessary to have supplementary 
material for every section in the standard, there are gaps 
in the numbering in the Commentary. 



Minimum Design Loads for Buildings and Other Structures 



231 



SECTION C1.0 

GENERAL 



SECTION C1.1 

SCOPE 

The minimum load requirements contained in this standard 
are derived from research and service performance of 
buildings and other structures. The user of this standard, 
however, must exercise judgment when applying the 
requirements to "other structures." Loads for some struc- 
tures other than buildings may be found in Sections 3 
through 10 of this Standard and additional guidance may 
be found in the Commentary. 

Both loads and load combinations are set forth in this 
document with the intent that they be used together. If one 
were to use loads from some other source with the load 
combinations set forth herein, or vice versa, the reliability 
of the resulting design may be affected. 

Earthquake loads contained herein are developed for 
structures that possess certain qualities of ductility and 
postelastic energy-dissipation capability. For this reason, 
provisions for design, detailing, and construction are pro- 
vided in Appendix A. In some cases, these provisions mod- 
ify or add to provisions contained in design specifications. 



SECTION C1 .3 

BASIC REQUIREMENTS 

Cl.3.1 Strength, Buildings and other structures must sat- 
isfy strength limit states in which members are proportioned 
to carry the design loads safely to resist buckling, yielding, 
fracture, and so on. It is expected that other standards pro- 
duced under consensus procedures and intended for use in 
connection with building code requirements will contain 
recommendations for resistance factors for strength design 
methods or allowable stresses (or safety factors) for allow- 
able stress design methods. 

Cl.3.2 Serviceability, In addition to strength limit states, 
buildings and other structures must also satisfy service- 
ability limit states that define functional performance and 
behavior under load and include such items as deflection 
and vibration. In the United States, strength limit states 
have traditionally been specified in building codes because 
they control the safety of the structure. Serviceability limit 
states, on the other hand, are usually noncatastrophic, define 
a level of quality of the structure or element, and are a 
matter of judgment as to their application. Serviceability 
limit states involve the perceptions and expectations of 
the owner or user and are a contractual matter between 
the owner or user and the designer and builder. It is for 



these reasons, and because the benefits themselves are often 
subjective and difficult to define or quantify, that service- 
ability limit states for the most part are not included within 
the three model U.S. Building Codes. The fact that ser- 
viceability limit states are usually not codified should not 
diminish their importance. Exceeding a serviceability limit 
state in a building or other structure usually means that its 
function is disrupted or impaired because of local minor 
damage or deterioration or because of occupant discomfort 
or annoyance. 

Cl.3.3 Self-Straining Forces. Constrained structures that 
experience dimensional changes develop self- straining 
forces. Examples include moments in rigid frames that 
undergo differential foundation settlements and shears in 
bearing wall that support concrete slabs that shrink. Unless 
provisions are made for self-straining forces, stresses in 
structural elements, either alone or in combination with 
stresses from external loads, can be high enough to cause 
structural distress. 

In many cases, the magnitude of self-straining forces 
can be anticipated by analyses of expected shrinkage, 
temperature fluctuations, foundation movement, and so 
on. However, it is not always practical to calculate the 
magnitude of self- straining forces. Designers often provide 
for self-straining forces by specifying relief joints, suitable 
framing systems, or other details to minimize the effects of 
self-straining forces. 

This section of this Standard is not intended to require 
the designer to provide for self- straining forces that cannot 
be anticipated during design. An example is settlement 
resulting from future adjacent excavation. 



SECTION C1 -4 
GENERAL STRUCTURAL INTEGRITY 

Through accident, misuse, or sabotage, properly designed 
structures may be subject to conditions that could lead to 
general or local collapse. Except for specially designed 
protective systems, it is usually impractical for a structure 
to be designed to resist general collapse caused by gross 
misuse of a large part of the system or severe abnormal 
loads acting directly on a large portion of it. However, 
precautions can be taken in the design of structures to limit 
the effects of local collapse and to prevent or minimize 
progressive collapse. Progressive collapse is defined as the 
spread of an initial local failure from element to element, 
eventually resulting in the collapse of an entire structure or 
a disproportionately large part of it. 



232 



ASCE 7-02 



Some authors have defined resistance to progressive 
collapse to be the ability of a structure to accommodate, 
with only local failure, the notional removal of any single 
structural member. Aside from the possibility of further 
damage that uncontrolled debris from the failed member 
may cause, it appears prudent to consider whether the 
abnormal event will fail only a single member. 

Since accidents, misuse, and sabotage are normally 
unforeseeable events, they cannot be defined precisely. 
Likewise, general structural integrity is a quality that cannot 
be stated in simple terms. It is the purpose of Section 1.4 
and this Commentary to direct attention to the problem of 
local collapse, present guidelines for handling it that will aid 
the design engineer, and promote consistency of treatment 
in all types of structures and in all construction materials. 
ASCE does not intend, at this time, for this standard to 
establish specific events to be considered during design, 
or for this standard to provide specific design criteria to 
minimize the risk of progressive collapse. 

Accidents, Misuse, Sabotage, and Their Consequences. 

In addition to unintentional or willful misuse, some of 
the incidents that may cause local collapse are [CI- 1] 1 : 
explosions due to ignition of gas or industrial liquids; boiler 
failures; vehicle impact; impact of falling objects; effects of 
adjacent excavations; gross construction errors; very high 
winds such as tornadoes; and sabotage. Generally, such 
abnormal events would not be a part of normal design 
considerations. The distinction between general collapse 
and limited local collapse can best be made by example 
as follows. 

General Collapse. The immediate, deliberate demolition 
of an entire structure by phased explosives is an obvious 
instance of general collapse. Also, the failure of one column 
in a 1-, 2-, 3-, or possibly even 4-column structure could 
precipitate general collapse, because the local failed column 
is a significant part of the total structural system at that 
level. Similarly, the failure of a major bearing element in 
the bottom story of a 2- or 3-story structure might cause 
general collapse of the whole structure. Such collapses are 
beyond the scope of the provisions discussed herein. There 
have been numerous instances of general collapse that have 
occurred as the result of such events as bombin landslides, 
and floods. 

Limited Local Collapse. An example of limited local 
collapse would be the containment of damage to adjacent 
bays and stories following the destruction of one or two 
neighboring columns in a multibay structure. The restriction 
of damage to portions of two or three stories of a higher 



1 Numbers in brackets refer to references listed at the ends 
of the major sections in which they appear (i.e., Section 1, 
Section 2, and so on). 



structure following the failure of a section of bearing wall 
in one story is another example. 

Examples of General Collapse. 

Ronan Point. A prominent case of local collapse that 
progressed to a disproportionate part of the whole building 
(and is thus an example of the type of failure of concern 
here) was the Ronan Point disaster, which brought the 
attention of the profession to the matter of general structural 
integrity in buildings. Ronan Point was a 22-story apartment 
building of large, precast concrete, load-bearing panels in 
Canning Town, England. In March 1968, a gas explosion in 
an 18th-story apartment blew out a living room wall. The 
loss of the wall led to the collapse of the whole corner of 
the building. The apartments above the 18th story, suddenly 
losing support from below and being insufficiently tied and 
reinforced, collapsed one after the other. The falling debris 
ruptured successive floors and walls below the 18th story, 
and the failure progressed to the ground. Better continuity 
and ductility might have reduced the amount of damage 
at Ronan Point. Another example is the failure of a 1- 
story parking garage reported in [CI -2]. Collapse of one 
transverse frame under a concentration of snow led to the 
later progressive collapse of the whole roof, which was 
supported by 20 transverse frames of the same type. Similar 
progressive collapses are mentioned in [CI -3]. 

Alfred P. Murrah Federal Building. [CI -4, CI -5, CI -6, 
Cl-7, Cl-8] On April 19, 1995, a truck containing approx- 
imately 4000 pounds of fertilizer-based explosive (ANFO) 
was parked near the sidewalk next to the 9-story rein- 
forced concrete office building. The side facing the blast 
had corner columns and four other perimeter columns. The 
blast shock wave disintegrated one of the 20 in. x 36 in. 
perimeter columns and caused brittle failures of two others. 
The transfer girder at the third level above these columns 
failed, and the upper-story floors collapsed in a progressive 
fashion. Approximately 70% of the building experienced 
dramatic collapse, and 168 people died, many of them as 
a direct result of progressive collapse. There might have 
been less damage had this structure not relied on transfer 
girders for support of upper floors, if there had been better 
detailing for ductility and greater redundancy, and if there 
had been better resistance for uplift loads on floor slabs. 

Following are a number of factors that contribute to the 
risk of damage propagation in modern structures [CI -9]: 

1. There is an apparent lack of general awareness 
among engineers that structural integrity against col- 
lapse is important enough to be regularly considered 
in design. 

2. In order to have more flexibility in floor plans and 
to keep costs down, interior walls and partitions are 



Minimum Design Loads for Buildings and Other Structures 



233 



often non- load-bearing and hence may be unable to 
assist in containing damage. 

3. In attempting to achieve economy in structure through 
greater speed of erection and less site labor, systems 
may be built with minimum continuity, ties between 
elements, and joint rigidity. 

4. Unreinforced or lightly reinforced load-bearing walls 
in multistory structures may also have inadequate 
continuity, ties, and joint rigidity. 

5. In roof trusses and arches, there may not be suffi- 
cient strength to carry the extra loads or sufficient 
diaphragm action to maintain lateral stability of the 
adjacent members if one collapses. 

6. In eliminating excessively large safety factors, code 
changes over the past several decades have reduced 
the large margin of safety inherent in many older 
structures. The use of higher-strength materials per- 
mitting more slender sections compounds the problem 
in that modern structures may be more flexible and 
sensitive to load variations and, in addition, may be 
more sensitive to construction errors. 

Experience has demonstrated that the principle of taking 
precautions in design to limit the effects of local collapse is 
realistic and can be satisfied economically. From a public 
safety viewpoint, it is reasonable to expect all multistory 
structures to possess general structural integrity comparable 
to that of properly designed, conventional framed structures 
[Cl-9, Cl-10]. 

Design Alternatives. There are a number of ways to 
obtain resistance to progressive collapse. In [CI -11], a 
distinction is made between direct and indirect design, and 
the following approaches are defined: 

Direct Design. Explicit consideration of resistance to pro- 
gressive collapse during the design process through either: 

Alternate Path Method, a method that allows local 
failure to occur, but seeks to provide alternate load paths 
so that the damage is absorbed and major collapse is 
averted, or 

Specific Local Resistance Method. A method that 
seeks to provide sufficient strength to resist failure from 
accidents or misuse. 

Indirect Design. Implicit consideration of resistance to 
progressive collapse during the design process through 
the provision of minimum levels of strength, continuity, 
and ductility. 

The general structural integrity of a structure may be 
tested by analysis to ascertain whether alternate paths 



around hypothetically collapsed regions exist. Alternatively, 
alternate path studies may be used as guides for developing 
rules for the minimum levels of continuity and ductility 
needed to apply the indirect design approach to enhance 
general structural integrity. Specific local resistance may 
be provided in regions of high risk, since it may be 
necessary for some element to have sufficient strength 
to resist abnormal loads in order for the structure as a 
whole to develop alternate paths. Specific suggestions for 
the implementation of each of the defined methods are 
contained in [CI- 11]. 

Guidelines for the Provision of General Structural 
Integrity. Generally, connections between structural com- 
ponents should be ductile and have a capacity for relatively 
large deformations and energy absorption under the effect 
of abnormal conditions. These criteria are met in many 
different ways, depending on the structural system used. 
Details that are appropriate for resistance to moderate wind 
loads and seismic loads often provide sufficient ductility. 
In 1999, ASCE issued a state of practice report that is a 
good introduction to the complex field of blast-resistant 
design [Cl-12]. 

Work with large precast panel structures [CI- 13, Cl- 
14, Cl-15] provides an example of how to cope with 
the problem of general structural integrity in a building 
system that is inherently discontinuous. The provision of 
ties combined with careful detailing of connections can 
overcome difficulties associated with such a system. The 
same kind of methodology and design philosophy can be 
applied to other systems [CI- 16]. The ACI Building Code 
Requirements for Structural Concrete [CI -17] includes such 
requirements in Section 7.13. 

There are a number of ways of designing for the required 
integrity to carry loads around severely damaged walls, 
trusses, beams, columns, and floors. A few examples of 
design concepts and details follow: 

1. Good plan layout. An important factor in achieving 
integrity is the proper plan layout of walls and 
columns. In bearing- wall structures there should 
be an arrangement of interior longitudinal walls to 
support and reduce the span of long sections of 
crosswall, thus enhancing the stability of individual 
walls and of the structures as a whole. In the case 
of local failure, this will also decrease the length of 
wall likely to be affected. 

2. Provide an integrated system of ties among the 
principal elements of the structural system. These 
ties may be designed specifically as components 
of secondary load-carrying systems, which often 
must sustain very large deformations during catas- 
trophic events. 

3. Returns on walls. Returns on interior and exterior 
walls will make them more stable. 



234 



ASCE 7-02 



4. Changing directions of span of floor slab. Where a 
floor slab is reinforced in order that it can, with a 
low safety factor, span in another direction if a load- 
bearing wall is removed, the collapse of the slab will 
be prevented and the debris loading of other parts 
of the structure will be minimized. Often, shrinkage 
and temperature steel will be enough to enable the 
slab to span in a new direction. 

5. Load-bearing interior partitions. The interior walls 
must be capable of carrying enough load to achieve 
the change of span direction in the floor slabs. 

6. Catenary action of floor slab. Where the slab cannot 
change span direction, the span will increase if an 
intermediate supporting wall is removed. In this 
case, if there is enough reinforcement throughout 
the slab and enough continuity and restraint, the 
slab may be capable of carrying the loads by 
catenary action, though very large deflections will 
result. 

7. Beam action of walls. Walls may be assumed to be 
capable of spanning an opening if sufficient tying 
steel at the top and bottom of the walls allows them 
to act as the web of a beam with the slabs above 
and below acting as flanges (see [CI- 13]). 

8. Redundant structural systems. Provide a secondary 
load path (e.g., an upper-level truss or transfer 
girder system that allows the lower floors of a 
multistory building to hang from the upper floors 
in an emergency) that allows framing to survive 
removal of key support elements. 

9. Ductile detailing. Avoid low ductility detailing in 
elements that might be subject to dynamic loads or 
very large distortions during localized failures (e.g., 
consider the implications of shear failures in beams 
or supported slabs under the influence of building 
weights falling from above). 

10. Provide additional reinforcement to resist blast and 
load reversal when blast loads are considered in 
design [CI- 18]. 

11, Consider the use of compartmentalized construc- 
tion in combination with special moment-resisting 
frames [CI -19] in the design of new buildings when 
considering blast protection. 

While not directly adding structural integrity for the 
prevention of progressive collapse, the use of special, 
nonfrangible glass for fenestration can greatly reduce risk 
to occupants during exterior blasts [CI- 18]. To the extent 
that nonfrangible glass isolates a building's interior from 
blast shock waves, it can also reduce damage to interior 
framing elements (e.g., supported floor slabs could be 
made to be less likely to fail due to uplift forces) for 
exterior blasts. 



SECTION C1 .5 

CLASSIFICATION OF BUILDINGS AND OTHER 

STRUCTURES 

Cl.5.1 Nature of Occupancy. The categories in Table 1-1 
are used to relate the criteria for maximum environmental 
loads or distortions specified in this standard to the conse- 
quence of the loads being exceeded for the structure and 
its occupants. The category numbering is unchanged from 
that in the previous edition of the standard (ASCE 7-98). 
Classification continues to reflect a progression of the antic- 
ipated seriousness of the consequence of failure from lowest 
hazard to human life (Category I) to highest (Category IV). 

In Sections 6, 7, 9, and 10, importance factors are 
presented for the four categories identified. The specific 
importance factors differ according to the statistical char- 
acteristics of the environmental loads and the manner in 
which the structure responds to the loads. The principle of 
requiring more stringent loading criteria for situations in 
which the consequence of failure may be severe has been 
recognized in previous versions of this standard by the spec- 
ification of mean recurrence interval maps for wind speed 
and ground snow load. 

This section now recognizes that there may be situations 
when it is acceptable to assign multiple categories to a 
structure based on use and the type of load condition being 
evaluated. For instance, there are circumstances when a 
structure should appropriately be designed for wind loads 
with importance factors greater than one, but would be 
penalized unnecessarily if designed for seismic loads with 
importance factors greater than one. An example would be 
a hurricane shelter in a low seismic area. The structure 
would be classified in Category IV for wind design and in 
Category II for seismic design. 

Category I contains buildings and other structures that 
represent a low hazard to human life in the event of failure 
either because they have a small number of occupants or 
have a limited period of exposure to extreme environmen- 
tal loadings. Examples of agricultural structures that fall 
under Category I are farm storage structures used exclu- 
sively for the storage of farm machinery and equipment, 
grain bins, corn cribs, and general purpose barns for the 
temporary feeding of livestock [CI -20]. Category II con- 
tains all occupancies other than those in Categories I, III, 
and IV and are sometimes referred to as "ordinary" for the 
purpose of risk exposure. Category III contains those build- 
ings and other structures that have large numbers of occu- 
pants, are designed for public assembly, or are designed for 
occupants who are restrained or otherwise restricted from 
movement, or are designed for evacuation. Buildings and 
other structures in Category III, therefore, represent a sub- 
stantial hazard to human life in the event of failure. 

Category IV contains buildings and other structures that 
are designated as essential facilities and are intended to 
remain operational in the event of extreme environmental 
loadings. Such occupancies include, but are not limited to, 



Minimum Design Loads for Buildings and Other Structures 



235 



hospitals and fire, rescue, and other emergency response 
facilities. Ancillary structures required for the operation 
of Category IV facilities during an emergency are also 
included in this category. In addition to essential facilities, 
buildings and other structures containing extremely haz- 
ardous materials have been added to Category IV to recog- 
nize the potential devastating effect a release of extremely 
hazardous materials may have on a population. 

Cl.5.2 Hazardous Materials and Extremely Hazardous 
Materials. A common method of categorizing structures 
storing hazardous materials or extremely hazardous mate- 
rials is by the use of a table of exempt amounts of these 
materials [CI -21, CI -22]. These and other references are 
sources of guidance on the identification of materials of 
these general classifications. A drawback to the use of tables 
of exempt amounts is the fact that the method cannot han- 
dle the interaction of multiple materials. Two materials may 
be exempt because alone neither poses a risk to the public, 
but may be deadly in a combined release. Therefore, an 
alternate and superior method of evaluating the risk to the 
public of a release of a material is by a hazard assessment 
as part of an overall risk management plan (RMP). 

Buildings and other structures containing hazardous 
materials or extremely hazardous materials may be clas- 
sified as Category II structures if it can be demonstrated 
that the risk to the public from a release of these materi- 
als is minimal. Companies that operate industrial facilities 
typically perform HAZOP (Hazard and Operability) stud- 
ies, conduct quantitative risk assessments, and develop risk 
management and emergency response plans. Federal regu- 
lations and local laws mandate many of these studies and 
plans [Cl-23]. Additionally, many industrial facilities are 
located in areas remote from the public and have restricted 
access, which further reduces the risk to the public. 

The risk management plan generally deals with mitigat- 
ing the risk to the general public. Risk to individuals outside 
the facility storing hazardous or extremely hazardous mate- 
rials is emphasized because plant personnel are not placed at 
as high a risk as the general public due to the plant person- 
nel's training in the handling of the hazardous or extremely 
hazardous materials and due to the safety procedures imple- 
mented inside the facilities. When these elements (trained 
personnel and safety procedures) are not present in a facil- 
ity, then the risk management plan must mitigate the risk 
to the plant personnel in the same manner as it mitigates 
the risk to the general public. 

As the result of the prevention program portion of 
a risk management plan, buildings and other structures 
normally falling into Category III may be classified into 
Category II if means (e.g., secondary containment) are 
provided to contain the hazardous materials or extremely 
hazardous materials in the case of a release. To qualify, 
secondary containment systems must be designed, installed, 
and operated to prevent migration of harmful quantities of 
toxic or explosive substances out of the system to the air, 



soil, ground water, or surface water at any time during 
the use of the structure. This requirement is not to be 
construed as requiring a secondary containment system to 
prevent a release of any toxic or explosive substance into 
the air. By recognizing that secondary containment shall 
not allow releases of "harmful" quantities of contaminants, 
this standard acknowledges that there are substances that 
might contaminate ground water but do not produce a 
sufficient concentration of hazardous materials or extremely 
hazardous materials during a vapor release to constitute a 
health or safety risk to the public. Because it represents 
the "last line of defense," secondary containment does not 
qualify for the reduced classification. 

If the beneficial effect of secondary containment can 
be negated by external forces, such as the overtopping of 
dike walls by floodwaters or the loss of liquid containment 
of an earthen dike due to excessive ground displacement 
during a seismic event, then the buildings or other struc- 
tures in question may not be classified into Category II. If 
the secondary containment is to contain a flammable sub- 
stance, then implementation of a program of emergency 
response and preparedness combined with an appropriate 
fire suppression system would be a prudent action associ- 
ated with a Category II classification. In many jurisdictions, 
such actions are required by local fire codes. 

Also as the result of the prevention program portion 
of a risk management plan, buildings and other struc- 
tures containing hazardous materials or extremely haz- 
ardous materials also could be classified as Category II 
for hurricane wind loads when mandatory procedures are 
used to reduce the risk of release of hazardous substances 
during and immediately after these predictable extreme 
loadings. Examples of such procedures include draining 
hazardous fluids from a tank when a hurricane is pre- 
dicted or, conversely, filling a tank with fluid to increase 
its buckling and overturning resistance. As appropriate to 
minimize the risk of damage to structures containing haz- 
ardous materials or extremely hazardous materials, manda- 
tory procedures necessary for the Category II classification 
should include preventative measures such as the removal 
of objects that might become air-borne missiles in the vicin- 
ity of the structure. 



SECTION C1. 7 

LOAD TESTS 

No specific method of test for completed construction 
has been given in this standard since it may be found 
advisable to vary the procedure according to conditions. 
Some codes require the construction to sustain a superim- 
posed load equal to a stated multiple of the design load 
without evidence of serious damage. Others specify that 
the superimposed load shall be equal to a stated multiple of 
the live load plus a portion of the dead load. Limits are set 
on maximum deflection under load and after removal of the 



236 



ASCE 7-02 



load. Recovery of at least three-quarters of the maximum 
deflection, within 24 hours after the load is removed, is a 
common requirement [CI- 17]. 



REFERENCES 

[Cl-1] Leyendecker, E.V., Breen, J.E., Somes, N.F., and 
Swatta, M. Abnormal loading on buildings and 
progressive collapse — An annotated bibliogra- 
phy. Washington, D.C.: U.S. Dept. of Commerce, 
National Bureau of Standards. NBS BSS 67, Jan. 
1976. 

[CI -2] Granstrom, S. and Carlsson, M. "Byggfurskningen 
T3: Byggnaders beteende vid overpaverkningar" 
[The behavior of buildings at excessive loadings]. 
Stockholm, Sweden: Swedish Institute of Building 
Research, 1974. 

[CI -3] Seltz-Petrash, A. "Winter roof collapses: bad luck, 
bad construction, or bad design?" Civil Engineer- 
ing, 42-45, Dec. 1979. 

[CI -4] Engineering News Record, (May 1, 1995). 

[C 1 -5] Federal Emergency Management Agency (FEMA). 
"The Oklahoma City Bombing: Improving Build- 
ing Performance through Multi-Hazard Mitiga- 
tion," FEMA 277, American Society of Civil 
Engineers and Federal Emergency Management 
Agency, 1996. 

[CI -6] Weidlinger, P. "Civilian structures: taking the 
defensive," Civil Engineering, Nov. 1994. 

[Cl-7] Longinow, A. "The threat of terrorism: can build- 
ings be protected?" Building Operating Manage- 
ment, July 1995, 

[CI -8] FEMA. "The Oklahoma City Bombing: Improving 
Building Performance through Multi-Hazard Mit- 
igation," FEMA 277, American Society of Civil 
Engineers and Federal Emergency Management 
Agency, 1996. 

[CI -9] Breen, J.E., ed. Progressive collapse of building 
structures [summary report of a workshop held 
at the University of Texas at Austin, Oct. 1975]. 
Washington, D.C.: U.S. Department of Housing 
and Urban Development. Rep. PDR-182, Sept. 
1976. 
[Cl-10] Burnett, E.F.P. The avoidance of progressive col- 
lapse: Regulatory approaches to the problem. 
Washington, D.C.: U.S. Department of Commerce, 
National Bureau of Standards. NBS GCR 75-48, 
Oct. 1975. [Available from: National Technical 
Information Service, Springfield, VA.] 
[Cl-11] Ellingwood, B.R. and Leyendecker, E.V. "Appro- 
aches for design against progressive collapse." J. 
Struct Div., 104(3), 413-423, 1978. 



[CI- 12] Mlakar, P. S. Structural Design for Physical Secu- 
rity: State of the Practice, Reston, VA: ASCE, 
1999. 

[Cl-13] Schultz, D.M., Burnett, E.F.P., and Fintel, M. A 
design approach to general structural integrity, 
design and construction of large-panel concrete 
structures. Washington, D.C.: U.S. Department of 
Housing and Urban Development, 1977. 

[CI- 14] PCI Committee on Precast Bearing Walls. "Con- 
siderations for the design of precast bearing-wall 
buildings to withstand abnormal loads." J. Pre- 
stressed Concrete Inst, 21(2): 46-69, March/ April 
1976. 

[CI- 15] Fintel, M. and Schultz, D.M. "Structural integrity 
of large-panel buildings." J. Am. Concrete Inst, 
76(5), 583-622, May 1979. 

[CI- 16] Fintel, M. and Annamalai, G. "Philosophy of 
structural integrity of multistory load-bearing con- 
crete masonry structures." J. Am. Concrete Inst, 
1(5), 27-35, May 1979. 

[Cl-17] American Concrete Institute (ACI). "Building 
Code Requirements for Structural Concrete," ACI 
Standard 318-02, American Concrete Institute 
Detroit, MI, 2002. 

[CI -18] ASCE. "Design of Blast Resistant Buildings in 
Petrochemical Facilities," ASCE Petrochemical 
Energy Committee, Task Committee on Blast 
Resistant Design, 1977. 

[Cl-19] FEMA. "NEHRP Recommended Provisions for 
Seismic Regulations for New Buildings and Other 
Structures," 1997 Edition, FEMA 302/Feb. 1998, 
Part 1 -Provisions, 1998. 

[Cl-20] FEMA. "Wet Floodproofing Requirements for 
Structures Located in Special Flood Hazard Areas 
in Accordance with the National Flood Insurance 
Program," Technical Bulletin 7-93, Federal 
Emergency Management Agency, Mitigation 
Directorate, Federal Insurance Administration, 
Washington, D.C., 1993. 

[CI -21] International Code Council. "2000 Internationa] 
Building Code," Tables 307.7(1) and 307.7(2), 
International Code Council, Falls Church, VA, 
2000. 

[CI -22] Environmental Protection Agency (EPA). "Emer- 
gency Planning and Notification — The List 
of Extremely Hazardous Substances and Their 
Threshold Planning Quantities," 40 CFR Part 355 
Appendix A, Environmental Protection Agency, 
Washington, D.C., July 1999. 

[CI -23] EPA. "Chemical Accident Prevention Provisions," 
40 CFR Part 68, Environmental Protection Agency, 
Washington, D.C., July 1999. 



Minimum Design Loads for Buildings and Other Structures 



237 



SECTION C2.0 

COMBINATIONS OF LOADS 



Loads in this standard are intended for use with design 
specifications for conventional structural materials includ- 
ing steel, concrete, masonry, and timber. Some of these 
specifications are based on allowable stress design, while 
others employ strength design. In the case of allowable 
stress design, design specifications define allowable stresses 
that may not be exceeded by load effects due to unfactored 
loads, that is, allowable stresses contain a factor of safety. 
In strength design, design specifications provide load fac- 
tors and, in some instances, resistance factors. Structural 
design specifications based on limit states design have been 
adopted by a number of specification-writing groups. There- 
fore, it is desirable to include herein common load factors 
that are applicable to these new specifications. It is intended 
that these load factors be used by all material-based design 
specifications that adopt a strength design philosophy in 
conjunction with nominal resistances and resistance fac- 
tors developed by individual material -specification- writing 
groups. Load factors given herein were developed using a 
first-order probabilistic analysis and a broad survey of the 
reliabilities inherent in contemporary design practice. Ref- 
erences [C2-9, C2-10, and C2-19] also provide guidelines 
for materials-specification-writing groups to aid them in 
developing resistance factors that are compatible, in terms 
of inherent reliability, with load factors and statistical infor- 
mation specific to each structural material. 

SECTION C2.2 
SYMBOLS AND NOTATION 

Self-straining forces can be caused by differential settle- 
ment foundations, creep in concrete members, shrinkage 
in members after placement, expansion of shrinkage- 
compensating concrete, and changes in temperature of 
members during the service life of the structure. In some 
cases, these forces may be a significant design consid- 
eration. In concrete or masonry structures, the reduction 
in stiffness that occurs upon cracking may relieve these 
self-straining forces, and the assessment of loads should 
consider this reduced stiffness. 

Some permanent loads, such as landscaping loads on 
plaza areas, may be more appropriately considered as live 
loads for purposes of design. 

SECTION C2.3 

COMBINING LOADS USING STRENGTH 

DESIGN 

C23.1 Applicability, Load factors and load combinations 
given in this section apply to limit states or strength design 



criteria (referred to as "Load and Resistance Factor Design" 
by the steel and wood industries), and they should not be 
used with allowable stress design specifications. 

C2.3.2 Basic Combinations. Unfactored loads to be used 
with these load factors are the nominal loads of Sections 3 
through 9 of this standard. Load factors are from NBS SP 
577 with the exception of the factor 1.0 for E, which is 
based on the more recent NEHRP research on seismic- 
resistant design [C2-21]. The basic idea of the load com- 
bination scheme is that in addition to dead load, which 
is considered to be permanent, one of the variable loads 
takes on its maximum lifetime value while the other vari- 
able loads assume "arbitrary point-in-time" values, the lat- 
ter being loads that would be measured at any instant 
of time [C2-23]. This is consistent with the manner in 
which loads actually combine in situations in which strength 
limit states may be approached. However, nominal loads in 
Sections 3 through 9 are substantially in excess of the arbi- 
trary point-in- time values. To avoid having to specify both 
a maximum and an arbitrary point-in-time value for each 
load type, some of the specified load factors are less than 
unity in combinations (2) through (6). 

Load factors in Section 2.3.2 are based on a survey 
of reliabilities inherent in existing design practice. The 
load factor on wind load in combinations (4) and (6) was 
increased to 1.6 in ASCE 7-98 from the value of 1.3 
appearing in ASCE 7-95. The reasons for this increase are 
twofold. 

First, the previous wind load factor, 1.3, incorporated 
a factor of 0.85 to account for wind directionality, that 
is, the reduced likelihood that the maximum wind speed 
occurs in a direction that is most unfavorable for building 
response [C2-12]. This directionality effect was not taken 
into account in ASD. Recent wind-engineering research 
has made it possible to identify wind directionality factors 
explicitly for a number of common structures. Accordingly, 
new wind directionality factors, K&, are presented in 
Table 6-6 of this standard; these factors now are reflected 
in the nominal wind forces, W, used in both strength design 
and allowable stress design. This change alone mandates an 
increase in the wind load factor to approximately 1.53. 

Second, the value in ASCE 7-95 of 1.3 was based on a 
statistical analysis of wind forces on buildings at sites not 
exposed to hurricane winds [C2-12]. Studies have shown 
that, owing to differences between statistical characteristics 
of wind forces in hurricane-prone coastal areas of the 
United States [C2-15, C2-16, and C2-17], the probability of 
exceeding the factored (or design-basis) wind force 1.3 W is 



Minimum Design Loads for Buildings and Other Structures 



239 



higher in hurricane-prone coastal areas than in the interior 
regions. Two recent studies [C2-13 and C2-14] have shown 
that the wind load factor in hurricane-prone areas should be 
increased to approximately 1.5 to 1.8 (depending on site) 
to maintain comparable reliability. 

To move toward uniform risk in coastal and inte- 
rior areas across the country, two steps were taken. 
First, the wind speed contours in hurricane-prone areas 
were adjusted to take the differences in extreme hurri- 
cane wind speed probability distributions into account (as 
explained in Section C6.5.4); these differences previously 
were accounted for in ASCE 7-95 by the "importance fac- 
tor." Second, the wind load factor was increased from 1.3 
to 1.6. This approach (a) reflects the removal of the direc- 
tionality factor, and (b) avoids having to specify separate 
load criteria for coastal and interior areas. 

Load combinations (6) and (7) apply specifically to cases 
in which the structural actions due to lateral forces and 
gravity loads counteract one another. 

Load factors given herein relate only to strength limit 
states. Serviceability limit states and associated load factors 
are covered in Appendix B of this standard. 

This Standard historically has provided specific proce- 
dures for determining magnitudes of dead, occupancy, live, 
wind, snow, and earthquake loads. Other loads not tradi- 
tionally considered by this standard may also require con- 
sideration in design. Some of these loads may be important 
in certain material specifications and are included in the 
load criteria to enable uniformity to be achieved in the load 
criteria for different materials. However, statistical data on 
these loads are limited or nonexistent, and the same proce- 
dures used to obtain load factors and load combinations in 
Section 2.3.2 cannot be applied at the present time. Accord- 
ingly, load factors for fluid load (F\ lateral pressure due 
to soil and water in soil (H), and self- straining forces and 
effects (T) have been chosen to yield designs that would 
be similar to those obtained with existing specifications if 
appropriate adjustments consistent with the load combina- 
tions in Section 2.3.2 were made to the resistance factors. 
Further research is needed to develop more accurate load 
factors because the load factors selected for H and F a , are 
probably conservative. 

Fluid load, F, defines structural actions in structural 
supports, framework, or foundations of a storage tank, 
vessel, or similar container due to stored liquid products. 
The product in a storage tank shares characteristics of both 
dead and live load. It is similar to a dead load in that its 
weight has a maximum calculated value, and the magnitude 
of the actual load may have a relatively small dispersion. 
However, it is not permanent; emptying and filling causes 
fluctuating forces in the structure, the maximum load may 
be exceeded by overfilling; and densities of stored products 
in a specific tank may vary. Adding F to combination 1 
provides additional conservatism for situations in which F 
is the dominant load. 



It should be emphasized that uncertainties in lateral 
forces from bulk materials, included in H, are higher 
than those in fluids, particularly when dynamic effects are 
introduced as the bulk material is set in motion by filling or 
emptying operations. Accordingly, the load factor for such 
loads is set equal to 1.6. 

C2.3.3 Load Combinations Including Flood Load. The 

nominal flood load, F at is based on the 100-year flood 
(Section 5.3.3.1). The recommended flood load factor of 
2.0 in V Zones and coastal A Zones is based on a statistical 
analysis of flood loads associated with hydrostatic pres- 
sures, pressures due to steady overland flow, and hydrody- 
namic pressures due to waves, as specified in Section 5.33. 

The flood load criteria were derived from an analysis 
of hurricane-generated storm tides produced along the U.S. 
East and Gulf coasts [C2-14], where storm tide is defined 
as the water level above mean sea level resulting from 
wind-generated storm surge added to randomly phased 
astronomical tides. Hurricane wind speeds and storm tides 
were simulated at 11 coastal sites based on historical 
storm climatology and on accepted wind speed and storm 
surge models. The resulting wind speed and storm tide 
data were then used to define probability distributions 
of wind loads and flood loads using wind and flood 
load equations specified in Sections 6.5, 5.3.3 and in 
other publications (U.S. Army Corps of Engineers). Load 
factors for these loads were then obtained using established 
reliability methods [C2-10] and achieve approximately the 
same level of reliability as do combinations involving wind 
loads acting without floods. The relatively high flood load 
factor stems from the high variability in floods relative to 
other environmental loads. The presence of 2.0 F a in both 
Eqs. 4 and 6 in V-Zones and Coastal A-Zones is the result 
of high stochastic dependence between extreme wind and 
flood in hurricane-prone coastal zones. The 2.0 F a also 
applies in coastal areas subject to northeasters, extra tropical 
storms, or coastal storms other than hurricanes where a high 
correlation exists between extreme wind and flood. 

Flood loads are unique in that they are initiated only 
after the water level exceeds the local ground elevation. 
As a result, the statistical characteristics of flood loads 
vary with ground elevation. The load factor 2.0 is based 
on calculations (including hydrostatic, steady flow, and 
wave forces) with still -water flood depths ranging from 
approximately 4 to 9 ft (average still-water flood depth of 
approximately 6 ft), and applies to a wide variety of flood 
conditions. For lesser flood depths, load factors exceed 2.0 
because of the wide dispersion in flood loads relative 
to the nominal flood load. As an example, load factors 
appropriate to water depths slightly less than 4 ft equal 
2.8 [C2-14]. However, in such circumstances, the flood load 
itself generally is small. Thus, the load factor 2.0 is based 
on the recognition that flood loads of most importance to 
structural design occur in situations where the depth of 
flooding is greatest. 



240 



ASCE 7-02 



C2.3 4 Load Combinations Including Atmospheric Ice 
Loads. Load combinations 1 and 2 in Sections 2.3.4 and 
2.4.3 include the simultaneous effects of snow loads as 
defined in Section 7 and Atmospheric Ice Loads as defined 
in Section 10. Load combinations 2 and 3 in Sections 2.3.4 
and 2.4.3 introduce the simultaneous effect of wind on the 
atmospheric ice. The wind load on the atmospheric ice, 
Wi, corresponds to approximately a 500-year MRL Accord- 
ingly, the load factors on W t and Di are set equal to 1.0 and 
0.7 in Sections 2.3.4 and 2.4.3, respectively: The rationale 
is exactly the same as that used to specify the earthquake 
force as 0.7 E in the load combinations applied in working 
stress design. The snow loads defined in Section 7 are based 
on measurements of frozen precipitation accumulated on the 
ground, which includes snow, ice due to freezing rain, and 
rain that falls onto snow and later freezes. Thus the effects 
of freezing rain are included in the snow loads for roofs, cat- 
walks, and other surfaces to which snow loads are normally 
applied. The atmospheric ice loads defined in Section 10 
are applied simultaneously to those portions of the structure 
on which ice due to freezing rain, in-cloud icing, or snow 
accrete that are not subject to the snow loads in Section 7. 
A trussed tower installed on the roof of a building is one 
example. The snow loads from Section 7 would be applied 
to the roof with the atmospheric ice loads from Section 10 
applied to the trussed tower. If a trussed tower has working 
platforms, the snow loads would be applied to the surface 
of the platforms with the atmospheric ice loads applied to 
the tower. If a sign is mounted on a roof, the snow loads 
would be applied to the roof and the atmospheric ice loads 
to the sign. 



SECTION C2.4 

COMBINING LOADS USING ALLOWABLE 

STRESS DESIGN 

C2.4.1 Basic Combinations. The load combinations listed 
cover those loads for which specific values are given in 
other parts of this standard. However, these combinations 
are not all-inclusive, and designers will need to exercise 
judgment in some situations. Design should be based on 
the load combination causing the most unfavorable effect. 
In some cases, this may occur when one or more loads are 
not acting. No safety factors have been applied to these 
loads since such factors depend on the design philosophy 
adopted by the particular material specification. 

Wind and earthquake loads need not be assumed to 
act simultaneously. However, the most unfavorable effects 
of each should be considered separately in design, where 
appropriate. In some instances, forces due to wind might 
exceed those due to earthquake, while ductility require- 
ments might be determined by earthquake loads. 

Load combinations (7) and (8) were new to the 1998 
edition of ASCE 7. They address the situation in which 
the effects of lateral or uplift forces counteract the effect 



of gravity loads. This eliminates an inconsistency in the 
treatment of counteracting loads in allowable stress design 
and strength design, and emphasizes the importance of 
checking stability. The earthquake load effect is multiplied 
by 0.7 to align allowable stress design for earthquake effects 
with the definition of E in Section 9.2.2.6, which is based 
on strength principles. 

Most loads, other than dead loads, vary significantly with 
time. When these variable loads are combined with dead 
loads, their combined effect should be sufficient to reduce 
the risk of unsatisfactory performance to an acceptably 
low level. However, when more than one variable load 
is considered, it is extremely unlikely that they will all 
attain their maximum value at the same time. Accordingly, 
some reduction in the total of the combined load effects 
is appropriate. This reduction is accomplished through the 
0.75 load combination factor. The 0.75 factor applies only 
to the variable loads, not to the dead load. 

Some material design standards that permit a one- third 
increase in allowable stress for certain load combinations 
have justified that increase by this same concept. Where 
that is the case, simultaneous use of both the one-third 
increase in allowable stress and the 25% reduction in 
combined loads is unsafe and is not permitted. In contrast, 
allowable stress increases that are based on duration of load 
or loading rate effects, which are independent concepts, 
may be combined with the reduction factor for combining 
multiple variable loads. Effects apply to the total stress; that 
is, the stress resulting from the combination of all loads. 
Load combination reduction factors for combined variable 
loads are different in that they apply only to the variable 
loads, and they do not affect the permanent loads or the 
stresses caused by permanent loads. This explains why the 
0.75 factor applied to the sum of all loads, to this edition, 
in which the 0.75 factor applies only to the sum of the 
variable loads, not the dead load. 

Certain material design standards permit a one-third 
increase in allowable stress for load combinations with one 
variable load where that variable is earthquake load. This 
standard handles allowable stress design for earthquake 
loads in a fashion to give results comparable to the strength 
design basis for earthquake loads as explained in the 
C.9 Commentary section titled "Use of Allowable Stress 
Design Standards." 

C2.4.2 Load Combinations Including Flood Load, The 
basis for the load combinations involving flood load is 
presented in detail in Section C2.3.3 on strength design. 
Consistent with the treatment of flood loads for strength 
design, F a has been added to load combinations (3) and (4); 
the multiplier on F a aligns allowable stress design for flood 
load with strength design. 

C2.4.3 Load Combinations Including; Atmospheric Ice 
Loads. See Section C2.3.4. 



Minimum Design Loads for Buildings and Other Structures 



241 



SECTION C2.5 
LOAD COMBINATIONS FOR 
EXTRAORDINARY EVENTS 

ASCE Standard 7 Commentary CI. 4 recommends ap- 
proaches to providing general structural integrity in build- 
ing design and construction. Commentary C2.5 explains the 
basis for the load combinations that the designer should use 
if the "Direct Design" alternative in Commentary CI. 4 is 
selected. If the authority having jurisdiction requires the 
"Indirect Design" alternative, that authority may use these 
load requirements as one basis for determining minimum 
required levels of strength, continuity, and ductility. Gener- 
ally, extraordinary events with a probability of occurrence 
in the range 10~ 6 to 10" 4 /yr or greater should be iden- 
tified, and measures should be taken to ensure that the 
performance of key loading-bearing structural systems and 
components is sufficient to withstand such events. 

Extraordinary events arise from extraordinary service or 
environmental conditions that traditionally are not consid- 
ered explicitly in design of ordinary buildings and struc- 
tures. Such events are characterized by a low probability 
of occurrence and usually a short duration. Few buildings 
are ever exposed to such events, and statistical data to 
describe their magnitude and structural effects are rarely 
available. Included in the category of extraordinary events 
would be fire, explosions of volatile liquids or natural gas in 
building service systems, sabotage, vehicular impact, mis- 
use by building occupants, subsidence (not settlement) of 
subsoil, and tornadoes. The occurrence of any of these 
events is likely to lead to structural damage or failure. 
If the structure is not properly designed and detailed, this 
local failure may initiate a chain reaction of failures that 
propagates throughout a major portion of the structure and 
leads to a potentially catastrophic collapse. Approximately 
15% to 20% of building collapses occur in this way [C2- 
1]. Although all buildings are susceptible to progressive 
failures in varying degrees, types of construction that lack 
inherent continuity and ductility are particularly vulnera- 
ble [C2-2, C2-22]. 

Good design practice requires that structures be robust 
and that their safety and performance not be sensitive to 
uncertainties in loads, environmental influences, and other 
situations not explicitly considered in design. The struc- 
tural system should be designed in such a way that if 
an extraordinary event occurs, the probability of dam- 
age disproportionate to the original event is sufficiently 
small [C2-7]. The philosophy of designing to limit the 
spread of damage rather than to prevent damage entirely 
is different from the traditional approach to designing to 
withstand dead, live, snow, and wind loads, but is similar 
to the philosophy adopted in modern earthquake-resistant 
design [C2-21]. 

In general, structural systems should be designed with 
sufficient continuity and ductility that alternate load paths 
can develop following individual member failure so that 



failure of the structure as a whole does not ensue. At a 
simple level, continuity can be achieved by requiring devel- 
opment of a minimum tie force — say 20 kN/m — between 
structural elements [C2-3]. Member failures may be con- 
trolled by protective measures that ensure that no essential 
load-bearing member is made ineffective as a result of 
an accident, although this approach may be more diffi- 
cult to implement. Where member failure would inevitably 
result in a disproportionate collapse, the member should be 
designed for a higher degree of reliability [C2-20]. In either 
approach, an enhanced quality assurance and maintenance 
program may be required. 

Design limit states include loss of equilibrium as a rigid 
body, large deformations leading to significant second-order 
effects, yielding or rupture of members of connections, 
formation of a mechanism, instability of members, or the 
structure as a whole. These limit states are the same as 
those considered for other load events, but the load-resisting 
mechanisms in a damaged structure may be different, and 
sources of load-carrying capacity that normally would not 
be considered in ordinary ultimate limit states design, such 
as a membrane or catenary action, may be included. The use 
of elastic analysis vastly underestimates the load-carrying 
capacity of the structure. Materially or geometrically non- 
linear or plastic analyses may be used, depending on the 
response of the structure to the actions. 

Specific design provisions to control the effect of 
extraordinary loads and risk of progressive failure can be 
developed with a probabilistic basis [C2-8 and C2-1 1]. One 
can either attempt to reduce the likelihood of the extraor- 
dinary event or design the structure to withstand or absorb 
damage from the event if it occurs. Let F be the event 
of failure and A be the event that a structurally damaging 
event occurs. The probability of failure due to event A is 



P f = P(F | A)P(A) 



(Eq. C2-1) 



in which P(F \ A) is the conditional probability of failure 
of a damaged structure and P(A) is the probability of 
occurrence of event A. The separation of P(F \ A) and 
P(A) allows one to focus on strategies for reducing risk. 
P(A) depends on siting, controlling the use of hazardous 
substances, limiting access, and other actions that are 
essentially independent of structural design. In contrast, 
P(F | A) depends on structural design measures ranging 
from minimum provisions for continuity to a complete post- 
damage structural evaluation. 

The probability, P(A), depends on the specific haz- 
ard. Limited data for severe fires, gas explosions, bomb 
explosions, and vehicular collisions indicate that the event 
probability depends on building size, measured in dwelling 
units or square footage, and ranges from about 0.23 x 
10~ 6 /d welling unit/year to about 7.8 x 10~ 6 /dwelling unit/ 
year [C2-6 and C2-8]. Thus, the probability that a building 
structure is affected depends on the number of dwelling 
units (or square footage) in the building. If one were 



242 



ASCE 7-02 



to set the conditional limit state probability, P(F \ A) = 
0.1 — 0.2/yr, however, the annual probability of structural 
failure from Eq. C2.5.1 would be on the order of 10~ 7 to 
10 -6 , placing the risk in the low-magnitude background 
along with risks from rare accidents [C2-24]. 

Design requirements corresponding to this desired P(F \ 
A) = 0.1 — 0.2 can be developed using first-order reliabil- 
ity analysis if the limit state function describing structural 
behavior is available [C2-10 and C2-19]. As an alternative, 
one can leave material and structural behavior considera- 
tions to the responsible material specifications and consider 
only the load combination aspect of the safety check, which 
is more straightforward. 

For checking a structure to determine its residual load- 
carrying capacity following occurrence of a damaging 
extraordinary event, selected load-bearing elements should 
be notionally removed and the capacity of the remaining 
structure evaluated using the following load combination: 

(0.9 or 1.2)D + (0.5L or 0.2S) + 0.2W (Eq. C2-2) 

For checking the capacity of a structure or structural 
element to withstand the effect of an extraordinary event, 
the following load combinations should be used; 



1.2D + A k + (0.5L or 0.25) 
(0.9 or l.2)D + A k + 0.2W 



(Eq. C2-3) 
(Eq. C2-4) 



The value of the load or load effect resulting from extraor- 
dinary event A used in design is denoted A k . Only limited 
data are available to define the frequency distribution of 
the load, and Ak must be specified by the authority having 
jurisdiction [C2-4]. The uncertainty in the load due to the 
extraordinary event is encompassed in the selection of a 
conservative Ak and thus the load factor on A* is set equal 
to 1.0, as is done in the earthquake load combinations in 
Section 2.3. Load factors less than 1.0 on the companion 
actions reflect the small probability of a joint occurrence of 
the extraordinary load and the design live, snow, or wind 
load. The companion action 0.5 L corresponds, approxi- 
mately, to the mean of the yearly maximum load [C2-5]. 
Companion actions 0.25 and 0.2W are interpreted similarly. 
A similar set of load combinations for extraordinary events 
appears in [C2-18]. 



REFERENCES 

[C2-1] Allen, D.E. and Schriever, W. "Progressive col- 
lapse, abnormal loads and building codes." Struc- 
tural Failures: Modes, Causes, Responsibilities, 
ASCE, New York, 21-48, 1973. 

[C2-2] Breen, J.E. and Siess, C.P. "Progressive col- 
lapse — symposium summary." J. Am. Concrete 
Inst, 76(9), 997-1004, 1979. 



[C2-3] British Standards Institution. "British standard 
structural use of steelwork in building." (BS 5950: 
Part 8), London, U.K., 1990. 
[C2-4] Burnett, E.F.P. "The avoidance of progressive 
collapse: Regulatory approaches to the problem." 
National Bureau of Standards Report GCR 75- 
48, Washington, D.C. (Available from National 
Technical Information Service, Springfield, Va.), 
1975. 
[C2-5] Chalk, P.L. and Corotis, R.B. "Probability models 
for design live loads." /. Struct. Div., ASCE, 
106(10), 2017-2033, 1980. 
[C2-6] CIB W14. "A conceptual approach towards a 
probability based design guide on structural fire 
safety." Fire Safety Journal 6(1) 1-79, 1983. 
[C2-7] "Commentary C Structural Integrity." National 
Building Code of Canada, National Research 
Council of Canada, Ottawa, Ontario, 1990. 
[C2-8] Ellingwood, B. and Leyendecker, E.V. "Appro- 
aches for design against progressive collapse." 7. 
Struct. Div., ASCE, 104(3), 413-423, 1978. 
[C2-9] Ellingwood, B., Galambos, T.V., MacGregor, J.G., 
and Cornell, C.A. "Development of a probability- 
based load criterion for American National Stan- 
dard A58." Washington, D.C: U.S. Dept. of 
Commerce, National Bureau of Standards, NBS 
SP 577, 1980. 

[C2-10] Ellingwood, B„ Galambos, T.V., MacGregor, J.G., 
and Cornell, C.A. "Probability-based load criteria: 
load factors and load combinations." J. Struct. 
Div., ASCE, 108(5), 978-997, 1982. 

[C2-11] Ellingwood, B. and Corotis, R.B. "Load combi- 
nations for buildings exposed to fires." Engrg. /., 
ASIC, 28(1), 37-44, 1991. 

[C2-12] Ellingwood, B. "Wind and snow load statistics 
for probabilistic design." J. Struct. Engrg., ASCE, 
107(7), 1345-1349, 1981. 

[C2-13] Ellingwood, B. And Tekie, P.B. "Wind load statis- 
tics for probability-based structural design." J. 
Struct Engrg., ASCE, 125(4), 453-464, 1999. 

[C2-14] Mehta, K.C., et al. "An investigation of load fac- 
tors for flood and combined wind and flood." 
Report prepared for Federal Emergency Manage- 
ment Agency, Washington, D.C, 1998. 

[C2-15] Peterka, J. A. and Shahid, S. "Design gust wind 
speeds in the United States." J. Struct. Engrg., 
ASCE, 124(2), 207-214, 1998. 

[C2-16] Vickery, P.J. and Twisdale, L.A. "Prediction of 
hurricane windspeeds in the United States." J. 
Struct Engrg., ASCE, 121(11), 1691-1699, 1995. 

[C2-17] Whalen, T. "Probabilistic estimates of design 
load factors for wind- sensitive structures using 
the 'peaks over threshold' approach." National 
Institute of Standards and Technology, NIST TN 
1418, Gaithersburg, Md., 1996. 



Minimum Design Loads for Buildings and Other Structures 



243 



[C2-18] Eurocode 1. "Common unified rules for different 
types of construction and material." Commission 
of the European Communities, Brussels, Belgium, 
1990. 

[C2-19] Galambos, T.V., Ellingwood, B., MacGregor, J.G., 
and Cornell, C.A. "Probability-based load criteria: 
assessment of current design practice." J. Struct. 
D/v., ASCE, 108(5), 959-977, 1982. 

[C2-20] Nordic Committee on Building Regulations (NKB). 
"Guidelines for loading and safety regulations for 
structural design." NKB Report No. 55E, Copen- 
hagen, Denmark, 1987. 



[C2-2 1 ] Federal Emergency Management Agency (FEMA). 
"NEHRP recommended provisions for the develop- 
ment of seismic regulations for buildings." FEMA 
Report 222, Washington, D.C., 1992. 

[C2-22] Taylor, D.A. "Progressive collapse." Can, J. Civ. 
Engrg., 2(4), 517-529, 1975. 

[C2-23] Turkstra, C J. and Madsen, H. "Load combinations 
for codified structural design." J. Struct. Div., 
ASCE, 106(12), 2527-2543, 1980. 

[C2-24] Wilson, R. and Crouch, E.A. "Risk assessment 
and comparisons: an introduction." Science, 236, 
267-270.1, 1987. 



244 



ASCE 7-02 



SECTION C3.0 

DEAD LOADS 



SECTION C3.2 

WEIGHTS OF MATERIALS AND 

CONSTRUCTIONS 

To establish uniform practice among designers, it is desir- 
able to present a list of materials generally used in build- 
ing construction, together with their proper weights. Many 
building codes prescribe the minimum weights for only a 
few building materials and, in other instances, no guide 
whatsoever is furnished on this subject. In some cases, the 
codes are so drawn up as to leave the question of what 
weights to use to the discretion of the building official, 
without providing any authoritative guide. This practice, as 
well as the use of incomplete lists, has been subjected to 
much criticism. The solution chosen has been to present, 
in this commentary, an extended list that will be useful 
to designer and official alike. However, special cases will 
unavoidably arise, and authority is therefore granted in the 
standard for the building official to deal with them. 

For ease of computation, most values are given in 
terms of pounds per square foot (lb/ft 2 ) (kN/m 2 ) of given 
thickness (see Table C3-1). Pounds per cubic foot (lb/ft 3 ) 
(kN/m 3 ) values, consistent with the pounds per square foot 
(kilonewtons per square meter) values, are also presented in 
some cases (see Table C3-2). Some constructions for which 
a single figure is given actually have a considerable range in 
weight. The average figure given is suitable for general use, 
but when there is reason to suspect a considerable deviation 
from this, the actual weight should be determined. 



Engineers, architects, and building owners are advised 
to consider factors that result in differences between actual 
and calculated loads. 

Engineers and architects cannot be responsible for cir- 
cumstances beyond their control. Experience has shown, 
however, that conditions are encountered which, if not con- 
sidered in design, may reduce the future utility of a building 
or reduce its margin of safety. Among them are: 

1. Dead Loads. There have been numerous instances 
in which the actual weights of members and con- 
struction materials have exceeded the values used in 
design. Care is advised in the use of tabular values. 
Also, allowances should be made for such factors as 
the influence of formwork and support deflections on 
the actual thickness of a concrete slab of prescribed 
nominal thickness. 

2. Future Installations. Allowance should be made for 
the weight of future wearing or protective surfaces 
where there is a good possibility that such may be 
applied. Special consideration should be given to the 
likely types and position of partitions, as insufficient 
provision for partitioning may reduce the future utility 
of the building. 

Attention is directed also to the possibility of temporary 
changes in the use of a building, as in the case of clearing 
a dormitory for a dance or other recreational purpose. 



Minimum Design Loads for Buildings and Other Structures 



245 



TABLE C3-1 
MINIMUM DESIGN DEAD LOADS* 



Component 



Load 
(psf) 



Component 



Load 
(psf) 



CEILINGS 

Acoustical Fiber Board 

Gypsum board (per mm thickness) 

Mechanical duct allowance 

Plaster on tile or concrete 

Plaster on wood lath 

Suspended steel channel system 

Suspended metal lath and cement plaster 

Suspended metal lath and gypsum plaster 

Wood furring suspension system 

COVERINGS, ROOF, AND WALL 

Asbestos-cement shingles 

Asphalt shingles 

Cement tile 

Clay tile (for mortar add 1 psf) 

Book tile, 2-in. 

Book tile, 3-in. 

Ludowici 

Roman 

Spanish 
Composition: 

Three-ply ready roofing 

Four-ply felt and gravel 

Five-ply felt and gravel 
Copper or tin 

Corrugated asbestos-cement roofing 
Deck, metal, 20 gage 
Deck, metal, 18 gage 



1 

0.55 

4 

5 

8 

2 

15 

10 

2.5 

4 

2 
16 

12 
20 
10 
12 
19 

1 

5.5 
6 
1 
4 

2.5 
3 



Decking, 2-in. wood (Douglas fir) 

Decking, 3-in. wood (Douglas fir) 

Fiberboard, 1/2-in. 

Gypsum sheathing, 1/2-in. 

Insulation, roof boards (per inch thickness) 

Cellular glass 

Fibrous glass 

Fiberboard 

Perlite 

Polystyrene foam 

Urethane foam with skin 
Plywood (per 1/8 -in. thickness) 
Rigid insulation, 1/2-in, 
Skylight, metal frame, 3/8-in. wire glass 
Slate, 3/16-in. 
Slate, 1/4-in. 
Waterproofing membranes: 

Bituminous, gravel-covered 

Bituminous, smooth surface 

Liquid applied 

Single-ply, sheet 
Wood sheathing (per inch thickness) 
Wood shingles 
FLOOR FILL 
Cinder concrete, per inch 
Lightweight concrete, per inch 
Sand, per inch 
Stone concrete, per inch 



0.75 

2 

0.7 

1.1 

1.5 

0.8 

0.2 

0.5 

0.4 

0.75 

8 

7 

10 

5.5 
1.5 

1 
0.7 

3 

3 



8 
12 



(continued) 



TABLE C3-1 - continued 
MINIMUM DESIGN DEAD LOADS* 



Component 



Load 
(psf) 



Component 



Load 
(psf) 



FLOORS AND FLOOR FINISHES 

Asphalt block (2-in.), 1/2-in. mortar 

Cement finish (1-in.) on stone- concrete fill 

Ceramic or quarry tile (3/4-in.) on 1/2-in. mortar bed 

Ceramic or quarry tile (3/4-in.) on 1-in. mortar bed 

Concrete fill finish (per inch thickness) 

Hardwood flooring, 111 -in. 

Linoleum or asphalt tile, 1/4-in. 

Marble and mortar on stone-concrete fill 

Slate (per mm thickness) 

Solid flat tile on 1-in. mortar base 

Subflooring, 3/4-in. 

Terrazzo (1- 1/2-in.) directly on slab 

Terrazzo (1-in.) on stone-concrete fill 

Terrazzo (1-in.), 2-in. stone concrete 

Wood block (3-in.) on mastic, no fill 

Wood block (3-in.) on 1/2-in. mortar base 

FLOORS, WOOD-JOIST (NO PLASTER) 

DOUBLE WOOD FLOOR 

Joist sizes 

(inches): 
2x6 
2x8 
2 x 10 
2x 12 
FRAME PARTITIONS 
Movable steel partitions 

Wood or steel studs, 1/2-in. gypsum board each side 
Wood studs, 2x4, unplastered 
Wood studs, 2 x 4, plastered one side 
Wood studs, 2x4, plastered two sides 
FRAME WALLS 
Exterior stud walls: 
2x4 @ 1.6-in., 5/8-in. gypsum, 

insulated, 3/8-in. siding 
2x6 @ 16-in., 5/8-in. gypsum, 

insulated, 3/8-in. siding 
Exterior stud walls with brick veneer 
Windows, glass, frame and sash 



12-in. 


16-in. 


24-in. 


spacing 


spacing 


spacing 


(lb/ft 2 ) 


(lb/ft 2 ) 


(lb/ft 2 ) 


6 


5 


5 


6 


6 


5 


7 


6 


6 


8 


7 


6 



30 
32 
16 
23 
12 
4 
1 

33 
15 
23 
3 

19 
32 
32 
1.0 
16 



4 
8 
4 
12 
20 



12 
48 



Clay brick wythes: 
4 in. 
8 in. 
12 in. 
16 in. 



Hollow concrete masonry unit wythes: 
Wythe thickness (in inches) 
Density of unit (16.49 kN/m 3 ) 
No grout 



48" o.c. 
40" o.c. 
32" o.c. 
24" o.c. 
16" o.c. 
Full Grout 



grout 
spacing 



Density of unit (125 pcf): 
No grout 



48" o.c. 




40" o.c. 


grout 


32" o.c. 


spacing 


24" o.c. 




16" o.c. 




Full Grout 





Density of unit (21.21 kN/m 3 ) 
No grout 



48" o.c. 
40" o.c. 
32" o.c. 
24" o.c 
1.6" o.c. 
Full Grout 



grout 
spacing 



Solid concrete masonry unit wythes (inci. 
Wythe thickness (in mm) 

Density of unit (105 pcf): 

Density of unit (125 pcf): 

Density of unit (135 pcf): 



39 

79 

115 

155 



4 


6 


8 


10 


12 


22 


24 


31 


37 


43 




29 


38 


47 


55 




30 


40 


49 


57 




32 


42 


52 


61 




34 


46 


57 


67 




40 


53 


66 


79 




55 


75 


95 


115 


26 


28 


36 


44 


50 




33 


44 


54 


62 




34 


45 


56 


65 




36 


47 


58 


68 




39 


51 


63 


75 




44 


59 


73 


87 




59 


81 


102 


123 


29 


30 


39 


47 


54 




36 


47 


57 


66 




37 


48 


59 


69 




38 


50 


62 


72 




41 


54 


67 


78 




46 


61 


76 


90 




62 


83 


105 


127 


4 


6 


8 


10 


12 


32 


51 


69 


87 


105 


38 


60 


81 


102 


124 


41 


64 


87 


110 


133 



* Weights of masonry include mortar but not plaster. For plaster, add 5 lb/ft 2 for each face plastered. Values given represent averages. In some cases, there is a considerable range of weight for the 
same construction. 



TABLE C3-1 
MINIMUM DESIGN DEAD LOADS* 



Component 



Load 
(kN/m 2 ) 



Component 



Load 
(kN/m 2 ) 



CEILINGS 

Acoustical fiberboard 

Gypsum board (per mm thickness) 

Mechanical duct allowance 

Plaster on tile or concrete 

Plaster on wood lath 

Suspended steel channel system 

Suspended metal lath and cement plaster 

Suspended metal lath and gypsum plaster 

Wood furring suspension system 

COVERINGS, ROOF, AND WALL 

Asbestos-cement shingles 

Asphalt shingles 

Cement tile 

Clay tile (for mortar add 0.48 kN/m 2 ) 

Book tile, 51 mm 

Book tile, 76 mm 

Ludowici 

Roman 

Spanish 
Composition: 

Three-ply ready roofing 

Four-ply felt and gravel 

Five-ply felt and gravel 
Copper or tin 

Corrugated asbestos-cement roofing 
Deck, metal, 20 gage 
Deck, metal, 18 gage 



0.05 

0.008 

0.19 

0.24 

0.38 

0.10 

0.72 

0.48 

0.12 

0.19 
0.10 

0.77 

0.57 
0.96 
0.48 
0.57 
0.91 

0.05 
0.26 
0.29 
0.05 
0.19 
0.12 
0.14 



Decking, 51 mm wood (Douglas fir) 

Decking, 76 mm wood (Douglas fir) 

Fiberboard, 13 mm 

Gypsum sheathing, 13 mm 

Insulation, roof boards (per mm thickness) 

Cellular glass 

Fibrous glass 

Fiberboard 

Perlite 

Polystyrene foam 

Urethane foam with skin 
Plywood (per mm thickness) 
Rigid insulation, 13 mm 
Skylight, metal frame, 10 mm wire glass 
Slate, 5 mm 
Slate, 6 mm 
Waterproofing membranes: 

Bituminous, gravel-covered 

Bituminous, smooth surface 

Liquid applied 

Single-ply, sheet 
Wood sheathing (per mm thickness) 
Wood shingles 
FLOOR FILL 
Cinder concrete, per mm 
Lightweight concrete, per mm 
Sand, per mm 
Stone concrete, per mm 



0.24 
0.38 
0.04 
0.10 

0.0013 

0.0021 

0.0028 

0.0015 

0.0004 

0.0009 

0.006 

0.04 

0.38 

0.34 

0.48 

0.26 

0.07 

0.05 

0.03 

0.0057 

0.14 

0.017 
0.015 
0.015 
0.023 



{continued) 



TABLE C3-1 - continued 
MINIMUM DESIGN DEAD LOADS* 



Component 



Load 
(kN/m 2 ) 



Component 



Load 
(kN/m 2 ) 



FLOORS AND FLOOR FINISHES 

Asphalt block (51 mm), 13 mm mortar 

Cement finish (25 mm) on stone-concrete fill 

Ceramic or quarry tile (19 mm) on 13 mm mortar bed 

Ceramic or quarry tile (19 mm) on 25 mm mortar bed 

Concrete fill finish (per mm thickness) 

Hardwood flooring, 22 mm 

Linoleum or asphalt tile, 6 mm 

Marble and mortar on stone-concrete fill 

Slate (per mm thickness) 

Solid flat tile on 25 mm mortar base 

Subflooring, 19 mm 

Terrazzo (38 mm) directly on slab 

Terrazzo (25 mm) on stone-concrete fill 

Terrazzo (25 mm), 51 mm stone concrete 

Wood block (76 mm) on mastic, no fill 

Wood block (76 mm) on 13 mm mortar base 

FLOORS, WOOD-JOIST (NO PLASTER) 

DOUBLE WOOD FLOOR 



Joist sizes 

(mm): 
51 x 152 
51 x 203 
51 x 254 
51 x 305 



305 mm 

spacing 

(kN/m 2 ) 

0.29 

0.29 

0.34 

0.38 



406 mm 

spacing 
(kN/m 2 ) 

0.24 

0.29 

0.29 

0.34 



610 mm 

spacing 

(kN/m 2 ) 

0.24 

0.24 

0.29 

0.29 



FRAME PARTITIONS 

Movable steel partitions 

Wood or steel studs, 13 mm gypsum board each side 

Wood studs, 51 x 102, unplastered 

Wood studs, 51 x 102, plastered one side 

Wood studs, 51 x 102, plastered two sides 

FRAME WALLS 

Exterior stud walls: 

51 mm x 102 mm @ 406 mm, 16 mm gypsum, 

insulated, 10 mm siding 
51 mm x 152 mm @ 406 mm, 16 mm gypsum, 

insulated, 10 mm siding 
Exterior stud walls with brick veneer 
Windows, glass, frame and sash 



1.44 

1.53 

0.77 

1.10 

0.023 

0.19 

0.05 

1.58 

0.028 

1.10 

0.14 

0.91 

1.53 

1.53 

0.48 

0.77 



0.19 
0.38 
0.19 
0.57 
0.96 



0.53 

0.57 

2.30 
0.38 



Clay brick wythes: 
102 mm 
203 mm 
305 mm 
406 mm 

Hollow concrete masonry unit wythes: 
Wythe thickness (in mm) 
Density of unit (16.49 kN/m 3 ) 

No grout 

1219 mm 

1016 mm grout 

813 mm spacing 

610 mm 

406 mm 

Full grout 

Density of unit (125 pcf): 
No grout 
1219 mm 

1016 mm grout 
813 mm spacing 

610 mm 
406 mm 
Full grout 

Density of unit (21.21 kN/m 3 ) 
No grout 
1219 mm 

1016 mm grout 

813 mm spacing 

610 mm 
406 mm 
Full grout 

Solid concrete masonry unit wythes (incl. concrete brick): 
Wythe thickness (in mm) 

Density of unit (16.49 kN/m 3 ) 

Density of unit (19.64 kN/m 3 ) 

Density of unit (21.21 kN/m 3 ) 



1.87 
3.78 
5.51 
7.42 



102 


152 


203 


254 


305 


1.05 


1.29 


1.68 


2.01 


2.35 




1.48 


1.92 


2.35 


2.78 




1.58 


2.06 


2.54 


3.02 




1.63 


2.15 


2.68 


3.16 




1.77 


2.35 


2.92 


3.45 




2.01 


2.68 


3.35 


4.02 




2.73 


3.69 


4.69 


5.70 


1.25 


1.34 


1.72 


2.11 


2.39 




1.58 


2.11 


2.59 


2.97 




1.63 


2.15 


2.68 


3.11 




1.72 


2.25 


2.78 


3.26 




1.87 


2.44 


3.02 


3.59 




2.11 


2.78 


3.50 


4.17 




2.82 


3.88 


4.88 


5.89 


1.39 


1.68 


2.15 


2.59 


3.02 




1.58 


2.39 


2.92 


3.45 




1.72 


2.54 


3.11 


3.69 




1.82 


2.63 


3.26 


3.83 




1.96 


2.82 


3.50 


4.12 




2.25 


3.16 


3.93 


4.69 




3.06 


4.17 


5.27 


6.37 


*ete brick): 








102 


152 


203 


254 


305 


1.53 


2.35 


3.21 


4.02 


4.88 


1.82 


2.82 


3.78 


4.79 


5.79 


1.96 


3.02 


4.12 


5.17 


6.27 



* Weights of masonry include mortar but not plaster. For plaster, add 0.24 kN/m 2 for each face plastered. Values given represent averages. In some cases, there is a considerable range of weight for 
the same construction. 



TABLE C3-2 
MINIMUM DENSITIES FOR DESIGN LOADS FROM MATERIALS 





Load 




Load 


Material 


(lb/ft 3 ) 


Material 


(lb/ft 3 ) 


Aluminum 


170 


Earth (submerged) 




Bituminous products 




Clay 


80 


Asphaltum 


81 


Soil 


70 


Graphite 


135 


River mud 


90 


Paraffin 


56 


Sand or gravel 


60 


Petroleum, crude 


55 


Sand or gravel and clay 


65 


Petroleum, refined 


50 


Glass 


160 


Petroleum, benzine 


46 


Gravel, dry 


104 


Petroleum, gasoline 


42 


Gypsum, loose 


70 


Pitch 


69 


Gypsum, wallboard 


50 


Tar 


75 


Ice 


57 


Brass 


526 


Iron 




Bronze 


552 


Cast 


450 


Cast-stone masonry (cement, stone, sand) 


144 


Wrought 


48 


Cement, portland, loose 


90 


Lead 


710 


Ceramic tile 


150 


Lime 




Charcoal 


12 


Hydrated, loose 


32 


Cinder fill 


57 


Hydrated, compacted 


45 


Cinders, dry, in bulk 


45 


Masonry, Ashlar stone 




Coal 




Granite 


165 


Anthracite, piled 


52 


Limestone, crystalline 


165 


Bituminous, piled 


47 


Limestone, oolitic 


135 


Lignite, piled 


47 


Marble 


173 


Peat, dry, piled 


23 


Sandstone 


144 


Concrete, plain 




Masonry, brick 




Cinder 


108 


Hard (low absorbtion) 


130 


Expanded- slag aggregate 


100 


Medium (medium absorbtion) 


115 


Haydite (burned-clay aggregate) 


90 


Soft (high absorbtion) 


100 


Slag 


132 


Masonry, concrete* 




Stone (including gravel) 


144 


Lightweight units 


105 


Vermiculite and perlite aggregate, non- load-bearing 


25-50 


Medium weight units 


125 


Other light aggregate, load-bearing 


70-105 


Normal weight units 


135 


Concrete, reinforced 




Masonry grout 


140 


Cinder 


111 


Masonry, rubble stone 




Slag 


138 


Granite 


153 


Stone (including gravel) 


150 


Limestone, crystalline 


147 


Copper 


556 


Limestone, oolitic 


138 


Cork, compressed 


14 


Marble 


156 


Earth (not submerged) 




Sandstone 


137 


Clay, dry 


63 


Mortar, cement or lime 


130 


Clay, damp 


110 


Particleboard 


45 


Clay and gravel, dry 


100 


Plywood 


36 


Silt, moist, loose 


78 


Riprap (Not submerged) 




Silt, moist, packed 


96 


Limestone 


83 


Silt, flowing 


108 


Sandstone 


90 


Sand and gravel, dry, loose 


100 


Sand 




Sand and gravel, dry, packed 


110 


Clean and dry 


90 


Sand and gravel, wet 


120 


River, dry 


106 



(continued) 



250 



ASCE 7-02 



TABLE C3-2 — continued 
MfNSMUM DENSITIES FOR DESIGN LOADS FROM MATERIALS 



Material 



Load 




Load 


(lb/ft 3 ) 


Material 


(lb/ft 3 ) 




Tin 


459 


70 


Water 




108 


Fresh 


62 


96 


Sea 


64 


52 


Wood, seasoned 




172 


Ash, commercial white 


41 


492 


Cypress, southern 


34 




Fir, Douglas, coast region 


34 


96 


Hem fir 


28 


95 


Oak, commercial reds and whites 


47 


82 


Pine, southern yellow 


37 


92 


Redwood 


28 


107 


Spruce, red, white, and Stika 


29 




Western hemlock 


32 


120 


Zinc, rolled sheet 


449 


72 







Slag 

Bank 

Bank screenings 

Machine 

Sand 
Slate 

Steel, cold-drawn 
Stone, quarried, piled 

Basalt, granite, gneiss 

Limestone, marble, quartz 

Sandstone 

Shale 

Greenstone, hornblende 
Terra cotta, architectural 

Voids filled 

Voids unfilled 



'Tabulated values apply to solid masonry and to the solid portion oi : hollow masonry. 



Minimum Design Loads for Buildings and Other Structures 



251 



TABLE C3-2 
MINIMUM DENSITIES FOR DESIGN LOADS FROM MATERIALS 





Load 




Load 


Material 


(kN/m 3 ) 


Material 


(kN/m 3 ) 


Aluminum 


170 


Earth (submerged) 




Bituminous products 




Clay 


12.6 


Asphaltum 


12.7 


Soil 


11.0 


Graphite 


21.2 


River mud 


14.1 


Paraffin 


8.8 


Sand or gravel 


9.4 


Petroleum, crude 


8.6 


Sand or gravel and clay 


10.2 


Petroleum, refined 


7.9 


Glass 


25.1 


Petroleum, benzine 


7.2 


Gravel, dry 


16.3 


Petroleum, gasoline 


6.6 


Gypsum, loose 


11.0 


Pitch 


10.8 


Gypsum, wallboard 


7.9 


Tar 


11.8 


Ice 


9.0 


Brass 


82.6 


Iron 




Bronze 


86.7 


Cast 


70.7 


Cast-stone masonry (cement, stone, sand) 


22.6 


Wrought 


75.4 


Cement, portland, loose 


14.1 


Lead 


111.5 


Ceramic tile 


23.6 


Lime 




Charcoal 


1.9 


Hydrated, loose 


5.0 


Cinder fill 


9.0 


Hydrated, compacted 


7.1 


Cinders, dry, in bulk 


7.1 


Masonry, Ashlar stone 




Coal 




Granite 


25.9 


Anthracite, piled 


8.2 


Limestone, crystalline 


25.9 


Bituminous, piled 


7.4 


Limestone, oolitic 


21.2 


Lignite, piled 


7.4 


Marble 


27.2 


Peat, dry, piled 


3.6 


Sandstone 


22.6 


Concrete, plain 




Masonry, brick 




Cinder 


17.0 


Hard (low absorbtion) 


20.4 


Expanded- slag aggregate 


15.7 


Medium (medium absorbtion) 


18.1 


Haydite (burned-clay aggregate) 


14.1 


Soft (high absorbtion) 


15.7 


Slag 


20.7 


Masonry, concrete* 




Stone (including gravel) 


22.6 


Lightweight units 


16.5 


Vermiculite and perlite aggregate, non- load-bearing 


3.9-7.9 


Medium weight units 


19.6 


Other light aggregate, load-bearing 


11.0-16.5 


Normal weight units 


21.2 


Concrete, reinforced 




Masonry grout 


22,0 


Cinder 


17.4 


Masonry, rubble stone 




Slag 


21.7 


Granite 


24.0 


Stone (including gravel) 


23.6 


Limestone, crystalline 


23.1 


Copper 


87.3 


Limestone, oolitic 


21.7 


Cork, compressed 


2.2 


Marble 


24.5 


Earth (not submerged) 




Sandstone 


21.5 


Clay, dry 


9.9 


Mortar, cement or lime 


20.4 


Clay, damp 


17.3 


Particleboard 


7.1 


Clay and gravel, dry 


15.7 


Plywood 


5.7 


Silt, moist, loose 


12.3 


Riprap (Not submerged) 




Silt, moist, packed 


15.1 


Limestone 


13.0 


Silt, flowing 


17.0 


Sandstone 


14.1 


Sand and gravel, dry, loose 


15.7 


Sand 




Sand and gravel, dry, packed 


17.3 


Clean and dry 


14.1 


Sand and gravel, wet 


18.9 


River, dry 


16.7 



(continued) 



252 



ASCE 7-02 



TABLE C3-2 - continued 
MINIMUM DENSITIES FOR DESIGN LOADS FROM MATERIALS 





Load 




Load 


Materia) 


(kN/m 3 ) 


Material 


(kN/m 3 ) 


Slag 




Tin 


72.1 


Bank 


11.0 


Water 




Bank screenings 


17.0 


Fresh 


9.7 


Machine 


15.1 


Sea 


10.1 


Sand 


8.2 


Wood, seasoned 




Slate 


27.0 


Ash, commercial white 


6.4 


Steel, cold-drawn 


77.3 


Cypress, southern 


5.3 


Stone, quarried, piled 




Fir, Douglas, coast region 


5.3 


Basalt, granite, gneiss 


15.1 


Hem fir 


4.4 


Limestone, marble, quartz 


14.9 


Oak, commercial reds and whites 


7.4 


Sandstone 


12.9 


Pine, southern yellow 


5.8 


Shale 


14.5 


Redwood 


4.4 


Greenstone, hornblende 


16.8 


Spruce, red, white, and Stika 


4.5 


Terra cotta, architectural 




Western hemlock 


5.0 


Voids filled 


18.9 


Zinc, rolled sheet 


70.5 


Voids unfilled 


11.3 







* Tabulated values apply to solid masonry and to the solid portion of hollow masonry. 



Minimum Design Loads for Buildings and Other Structures 



253 



SECTION 04,0 

IIWE LOADS 



SECTION C4.2 
UNIFORMLY DISTRIBUTED LOADS 

C4.2.1 Required Live Loads. A selected list of loads 
for occupancies and uses more commonly encountered is 
given in Section 4.2.1, and the authority having jurisdiction 
should approve on occupancies not mentioned. Tables C4-1 
and C4-2 are offered as a guide in the exercise of 
such authority. 

In selecting the occupancy and use for the design 
of a building or a structure, the building owner should 
consider the possibility of later changes of occupancy 
involving loads heavier than originally contemplated. 
The lighter loading appropriate to the first occupancy 
should not necessarily be selected. The building owner 
should ensure that a live load greater than that for 
which a floor or roof is approved by the authority hav- 
ing jurisdiction is not placed, or caused, or permitted 
to be placed on any floor or roof of a building or 
other structure. 

In order to solicit specific informed opinion regarding 
the design loads in Table 4-1, a panel of 25 distinguished 
structural engineers was selected. A Delphi [C4-1] was 
conducted with this panel in which design values and sup- 
porting reasons were requested for each occupancy type. 
The information was summarized and recirculated back to 
the panel members for a second round of responses; those 
occupancies for which previous design loads were reaf- 
firmed, as well as those for which there was consensus 
for change, were included. 

It is well known that the floor loads measured in a 
live-load survey usually are well beiow present design val- 
ues [C4-2-C4-5]. However, buildings must be designed 
to resist the maximum loads they are likely to be sub- 
jected to during some reference period T, frequently taken 
as 50 years. Table C4-2 briefly summarizes how load sur- 
vey data are combined with a theoretical analysis of the 
load process for some common occupancy types and illus- 
trates how a design load might be selected for an occupancy 
not specified in Table 4-1 [C4-6]. The floor load normally 
present for the intended functions of a given occupancy 
is referred to as the sustained load. This load is modeled 
as constant until a change in tenant or occupancy type 
occurs. A live-load survey provides the statistics of the sus- 
tained load. Table C4-2 gives the mean, m s , and standard 
deviation, cr x , for particular reference areas. In addition to 
the sustained load, a building is likely to be subjected 
to a number of relatively short-duration, high-intensity, 
extraordinary, or transient loading events (due to crowd- 
ing in special or emergency circumstances, concentrations 



during remodeling, and the like). Limited survey informa- 
tion and theoretical considerations lead to the means, m t , 
and standard deviations, a t , of single transient loads shown 
in Table C4-2. 

Combination of the sustained load and transient load pro- 
cesses, with due regard for the probabilities of occurrence, 
leads to statistics of the maximum total load during a speci- 
fied reference period T. The statistics of the maximum total 
load depend on the average duration of an individual ten- 
ancy, r, the mean rate of occurrence of the transient load, 
v e , and the reference period, T. Mean values are given in 
Table C4-2. The mean of the maximum load is similar, 
in most cases, to the Table 4-1 values of minimum uni- 
formly distributed live loads and, in general, is a suitable 
design value. 

For library stack rooms, the 150 psf (7.18 kN/m) uni- 
form live load specified in Table 4-1 is intended to cover 
the range of ordinary library shelving. The most important 
variables that affect the floor loading are the book stack 
unit height and the ratio of the shelf depth to the aisle 
width. Common book stack units have a nominal height of 
90 in. (2290 mm) or less, with shelf depths in the range 
of 8 in. (203 mm) to 12 in. (305 mm). Book weights vary, 
depending on their size and paper density, but there are 
practical limits to what can be stored in any given space. 
Book stack weights also vary, but not by enough to sig- 
nificantly affect the overall loading. Considering the prac- 
tical combinations of the relevant dimensions, weights, and 
other parameters, if parallel rows of ordinary double-faced 
book stacks are separated by aisles that are at least 36 in. 
(914 mm) wide, then the average floor loading is unlikely 
to exceed the specified 150 psf (7.18 kN/m 2 ), even after 
allowing for a nominal aisle floor loading of 20 to 40 psf 
(0.96 to 1.92 kN/m 2 ). 

The 150 psf floor loading is also applicable to typical file 
cabinet installations, provided that the 36 in. minimum aisle 
width is maintained. Five-drawer lateral or conventional 
file cabinets, even with two levels of book shelves stacked 
above them, are unlikely to exceed the 150 psf average 
floor loading unless all drawers and shelves are filled to 
capacity with maximum density paper. Such a condition 
is essentially an upper-bound for which the normal load 
factors and safety factors applied to the 150 psf criterion 
should still provide a safe design. 

If a library shelving installation does not fall within 
the parameter limits that are specified in footnote 3 
of Table 4-1, then the design should account for the 
actual conditions. For example, the floor loading for stor- 
age of medical X-ray film may easily exceed 200 psf 
(2.92 kN/m 2 ), mainly because of the increased depth of 



254 



ASCE 7-02 



the shelves. Mobile library shelving that rolls on rails 
should also be designed to meet the actual requirements of 
the specific installation, which may easily exceed 300 psf 
(14.4 kN/m 2 ). The rail support locations and deflection lim- 
its should be considered in the design, and the engineer 
should work closely with the system manufacturer in order 
to provide a serviceable structure. 



SECTION C4.3 
CONCENTRATED LOADS 

C4.3.1 Accessible Roof-Supporting Members. The pro- 
vision regarding concentrated loads supported by roof 
trusses or other primary roof members is intended to pro- 
vide for a common situation for which specific requirements 
are generally lacking. 



SECTION C4.6 
PARTIAL LOADING 

It is intended that the full intensity of the appropriately 
reduced live load over portions of the structure or member 
be considered, as well as a live load of the same intensity 
over the full length of the structure or member. 

Partial-length loads on a simple beam or truss will 
produce higher shear on a portion of the span than a 
full-length load. "Checkerboard" loadings on multistoried, 
multipanel bents will produce higher positive moments than 
full loads, while loads on either side of a support will 
produce greater negative moments. Loads on the half span 
of arches and domes or on the two central quarters can 
be critical. For roofs, all probable load patterns should be 
considered/Cantilevers cannot rely on a possible live load 
on the anchor span for equilibrium. 



SECTION C4.4 

LOADS ON HANDRAILS, GUARDRAIL 

SYSTEMS, GRAB BAR SYSTEMS, AND 

VEHICLE BARRIER SYSTEMS 

C4A2 Loads. 

a. Loads that can be expected to occur on handrail 
and guardrail systems are highly dependent on the 
use and occupancy of the protected area. For cases 
in which extreme loads can be anticipated, such as 
long straight runs of guardrail systems against which 
crowds can surge, appropriate increases in loading 
shall be considered. 

b. When grab bars are provided for use by persons 
with physical disabilities, the design is governed 
by CABO A117, Accessible and Usable Buildings 
and Facilities. 

c. Vehicle barrier systems may be subjected to hori- 
zontal loads from moving vehicles. These horizontal 
loads may be applied normal to the plane of the 
barrier system, parallel to the plane of the barrier sys- 
tem, or at any intermediate angle. Loads in garages 
accommodating trucks and buses may be obtained 
from the provisions contained in Standard Speci- 
fications for Highway Bridges, 1989, The Ameri- 
can Association of State Highway and Transporta- 
tion Officials. 

d. This provision was introduced into the standard in 
1998 and is consistent with the provisions for stairs. 

e. Side rail extensions of fixed ladders are often flexible 
and weak in the lateral direction. OSHA (CFR 1910) 
requires side rail extensions with specific geometric 
requirements only. The load provided was introduced 
into the standard in 1998, and has been determined 
on the basis of a 250-lb person standing on a rung of 
the ladder, and accounting for reasonable angles of 
pull on the rail extension. 



SECTION C4.7 
IMPACT LOADS 

Grandstands, stadiums, and similar assembly structures may 
be subjected to loads caused by crowds swaying in unison, 
jumping to its feet, or stomping. Designers are cautioned 
that the possibility of such loads should be considered. 

SECTION C4.8 
REDUCTION IN LIVE LOADS 

C4.8.1 General, The concept of, and methods for, deter- 
mining member live load reductions as a function of a 
loaded member's influence area, A/, was first introduced 
into this standard in 1982, and was the first such change 
since the concept of live load reduction was introduced over 
40 years ago. The revised formula is a result of more exten- 
sive survey data and theoretical analysis [C4-7]. The change 
in format to a reduction multiplier results in a formula that 
is simple and more convenient to use. The use of influence 
area, now defined as a function of the tributary area, A t , in 
a single equation has been shown to give more consistent 
reliability for the various structural effects. The influence 
area is defined as that floor area over which the influ- 
ence surface for structural effects is significantly different 
from zero. 

The factor K LL is the ratio of the influence area (A/) 
of a member to its tributary area (At), i.e.: K LL = Ail At, 
and is used to better define the influence area of a mem- 
ber as a function of its tributary area. Figure C4 illus- 
trates typical influence areas and tributary areas for a 
structure with regular bay spacings. Table 4-2 has estab- 
lished Kn values (derived from calculated Kn values) 
to be used in Eq. 4-1 for a variety of structural mem- 
bers and configurations. Calculated K LL values vary for 
column and beam members having adjacent cantilever con- 
struction, as is shown in Figure C4, and the Table 4-2 
values have been set for these cases to result in live 



Minimum Design Loads for Buildings and Other Structures 



255 



load reductions that are slightly conservative. For unusual 
shapes, the concept of significant influence effect should 
be applied. 

An example of a member without provisions for contin- 
uous shear transfer normal to its span would be a precast 
T-beam or double T beam, which may have an expansion 
joint along one or both flanges, or which may have only 
intermittent weld tabs along the edges of the flanges. Such 
members do not have the ability to share loads located 
within their tributary areas with adjacent members, thus 
resulting in Kll, = 1 for these types of members. 

Reductions are permissible for two-way slabs and for 
beams, but care should be taken in defining the appropriate 
influence area. For multiple floors, areas for members 
supporting more than one floor are summed. 

The formula provides a continuous transition from 
unreduced to reduced loads. The smallest allowed value 
of the reduction multiplier is 0.4 (providing a maximum 
60% reduction), but there is a minimum of 0.5 (providing a 
50% reduction) for members with a contributory load from 
just one floor. 

C4.8.2 Heavy Live Loads- In the case of occupancies 
involving relatively heavy, basic live loads such as storage 
buildings, several adjacent floor panels may be fully loaded. 
However, data obtained in actual buildings indicate that 
rarely is any story loaded with an average actual live load 
of more than 80% of the average rated live load. It appears 
that the basic live load should not be reduced for the floor- 
and-beam design, but that it could be reduced a flat 20% 
for the design of members supporting more than one floor. 
Accordingly, this principle has been incorporated into the 
recommended requirement. 

C4.8.3 Parking Garage Loads, Unlike live loads in office 
and residential buildings, which are generally spatially 
random, parking garage loads are due to vehicles parked 
in regular patterns and the garages are often full. The 
rationale behind the reduction according to area for other 
live loads therefore does not apply. A load survey of vehicle 
weights was conducted at nine commercial parking garages 
in four cities of different sizes [C4-13]. Statistical analyses 
of the maximum load effects on beams and columns due 
to vehicle loads over the garage's life were carried out 
using the survey results. Dynamic effects on the deck 
due to vehicle motions and on the ramp due to impact 
were investigated. The equivalent uniformly distributed 
loads (EUDL) that would produce the lifetime maximum 
column axial force and midspan beam bending moment 
are conservatively estimated at 34.8 psf. The EUDL is not 
sensitive to bay-size variation. In view of the possible 
impact of very heavy vehicles in the future such as 
sport-utility vehicles, however, a design load of 40 psf is 
recommended with no allowance for reduction according 
to bay area. 



Compared with the design live load of 50 psf given 
in previous editions of the Standard, the design load 
contained herein represents a 20% reduction but is still 
33% higher than the 30 psf one would obtain were an area- 
based reduction to be applied to the 50 psf value for large 
bays as allowed in most Standards. Also, the variability 
of the maximum parking garage load effect is found to 
be small with a coefficient of variation less than 5% in 
comparison with 20% to 30% for most other live loads. The 
implication is that when a live load factor of 1 .6 is used in 
design, additional conservatism is built into it such that the 
recommended value would also be sufficiently conservative 
for special purpose parking (such as valet parking) where 
vehicles may be more densely parked causing a higher load 
effect. Therefore, the 50 psf design value was thought to be 
overly conservative and it can be reduced to 40 psf without 
sacrificing structural integrity. 

In view of the large load effect produced by a single 
heavy vehicle (up to 10,000 lb), the current concentrated 
load of 2000 lb should be increased to 3000 lb acting on an 
area of 4.5 in. by 4.5 in., which represents the load caused 
by a jack in changing tires. 

C4.8.5 Limitations on One- Way Slabs. One-way slabs 
behave in a manner similar to two-way slabs, but do not 
benefit from having a higher redundancy which results from 
two-way action. For this reason, it is appropriate to allow 
a live load reduction for one-way slabs, but restrict the 
tributary area, A T , to an area which is the product of the 
slab span times a width normal to the span not greater than 
1.5 times the span (thus resulting in an area with an aspect 
ratio of 1.5). For one-way slabs with aspect ratios greater 
than 1.5, the effect will be to give a somewhat higher live 
load (where a reduction has been allowed) than for two-way 
slabs with the same ratio. 

Members such as hollow-core slabs, which have grouted 
continuous shear keys along their edges and that span in 
one direction only, are considered as one-way slabs for 
live load reduction even though they may have continuous 
shear transfer normal to their span. 



SECTION C4.9 
MINIMUM ROOF LIVE LOADS 

C4.9.1 Flat, Pitched, and Curved Roofs. The values 
specified in Eq. 4-2 that act vertically upon the projected 
area have been selected as minimum roof live loads, even 
in localities where little or no snowfall occurs. This is 
because it is considered necessary to provide for occasional 
loading due to the presence of workers and materials during 
repair operations. 

C4.9.2 Special Purpose Roofs. Designers should consider 
any additional dead loads that may be imposed by saturated 
landscaping materials. Special purpose or occupancy roof 



256 



ASCE 7-02 



live loads may be reduced in accordance with the require- 
ments of Section 4.8. 

SECTION C4.10 
CRANE LOADS 

All support components of moving bridge cranes and 
monorail cranes including runway beams, brackets, bracing, 
and connections shall be designed to support the maximum 
wheel load of the crane and the vertical impact, lateral, 
and longitudinal forces induced by the moving crane. Also, 
the runway beams shall be designed for crane stop forces. 
The methods for determining these loads vary depending 
on the type of crane system and support. See [C4-8 to 
C4-11], which describe types of bridge cranes and monorail 
cranes. Cranes described in these references include top 
running bridge cranes with top running trolley, underhung 
bridge cranes, and underhung monorail cranes. [C4-12] 
gives more stringent requirements for crane runway design 
that are more appropriate for higher capacity or higher 
speed crane systems. 

REFERENCES 

[C4-1] Corotis, R.B., Fox, R.R., and Harris, J.C. "Delphi 

methods: Theory and design load application." ./. 

Struct Div., ASCE, 107(ST6), 1095-1105, 1981. 
[C4-2] Peir, J.C. and Cornell, C.A. "Spatial and temporal 

variability of live loads." /. Struct Div., ASCE, 

99(ST5), 903-922, 1973. 
[C4-3] McGuire, R.K. and Cornell, C.A. "Live load 

effects in office buildings." J. Struct Div., ASCE, 

100(ST7), 1351-1366, 1974. 



[C4-4] Ellingwood, B.R. and Culver, C.G. "Analysis of 
live loads in office buildings." J, Struct Div., 
ASCE, 103(ST8), 1551-1560, 1977. 
[C4-5] Sentler, L. A stochastic model for live loads on 
floors in buildings. Lund Institute of Technol- 
ogy, Division of Building Technology, Report 60, 
Lund, Sweden, 1975. 
[C4-6] Chalk, P.L. and Corotis, R.B. "A probability 
model for design live loads." J. Struct Div., 
ASCE, 106(ST10), 2017-2030, 1980. 
[C4-7] Harris, M.E., Corotis, R.B., and Bova, CJ. "Area- 
dependent processes for structural live loads." J. 
Struct Div., ASCE, 107(ST5), 857-872, 1981. 
[C4-8] Material Handling Industry. "Specifications for 
Underhung Cranes and Monorail Systems." ANSI 
MH 27.1, Charlotte, N.C., 1981. 
[C4-9] Material Handling Industry. "Specifications for 
Electric Overhead Traveling Cranes." No. 70, 
Charlotte, N.C., 1994. 

[C4-10] Material Handling Industry. "Specifications for 
Top Running and Under Running Single Girder 
Electric Overhead Traveling Cranes." No. 74, 
Charlotte, N.C., 1994. 

[C4-11] Metal Building Manufacturers Association (MB 
MA). Low Rise Building Systems Manual, Cleve- 
land, Ohio, 1986. 

[C4-12] Association of Iron and Steel Engineers. Technical 
Report No. 13, Pittsburgh, Penn., 1979. 

[C4-13] Wen, Y. K. and Yeo, G. L. "Design live loads for 
passenger cars parking garages." J. Struct Engrg., 
ASCE, 127(3), 2001. (Based on "Design Live 
Loads for Parking Garages," ASCE, Reston, Va., 
1999.) 



Minimum Design Loads for Buildings and Other Structures 



257 



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Element 


Actual K^ 

Members 

w/o 

Cantifevers 


Actual 1^ 

Members 

w/ Cantilevers 


(Table 4-2) 


Example 
Member 
(Rg. C-4) 


n = 


n = 0.5 


n = 1.0 


Interior Columns 


4 


- 


- 




4 


E4 


Exterior Columns w/o cantilevers 


4 


- 


_J_J 


- 


4 


G7.J6 


Edge Columns w/ cantilevers 




4 


3 


2.67 


3 


B3 


Corner Columns w/ cantilevers 


- 


4 


2.25 


1.78 


2 


K2 


Edge Beams w/o cantilever stabs 


2 


- 


- 


- 


2 


07 - E7 


interior Beams 


2 




- 


- 


2 


H4-H5 


Edge Beams w/ cantilever slabs 


- 


2 


1.5 


1.33 


1 


B5-B6 


Cantilever Beams w/o cantilever slabs 


2 


- 


- 


- 


1 


E1 -E2 


Cantilever Beams w/ cantilever slabs 


- 


2* 


1.5* 


1-33* 


1 


K5-L5 






Limits of 
Influence Area 

Limits of 
Tributary Area 



• The value of n for member K5-L5 is used to calculate the distance nLn 



FIGURE C4 
TYPICAL TRIBUTARY AND INFLUENCE AREAS 



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TABLE C4-1 
MINIMUM UNIFORMLY DISTRIBUTED LIVE LOADS 



Occupancy or use 



Live Load 
lb/ft 2 (kN/m 2 ) 



Occupancy or use 



Live Load 

lb/ft 2 (kN/m 2 ) 



Air-conditioning (machine space) 
Amusement park structure 
Attic, Nonresidential 

Nonstorage 

Storage 
Bakery 

Exterior 

Interior (fixed seats) 

Interior (movable seats) 
Bpathouse, floors 
Boiler room, framed 
Broadcasting studio 
Catwalks 

Ceiling, accessible furred 
Cold Storage 

No overhead system 

Overhead system 
Floor 
Roof 
Computer equipment 
Courtrooms 
Dormitories 

Nonpartitioned 

Partitioned 
Elevator machine room 
Fan room 
File room 

Duplicating equipment 

Card 

Letter 
Foundries 

Fuel rooms, framed 
Garages — trucks 
Greenhouses 
Hangars 

Incinerator charging floor 
Kitchens, other than domestic 



200* (9.58) 
100* (4.79) 

25 (1.20) 
80* (3.83) 
150 (7.18) 
100 (4.79) 
60 (2.87) 
100 (4.79) 
100* (4.79) 
300* (14.36) 
100 (4.79) 
25 (1.20) 
10 # (0.48) 

250" (11.97) 

150 (7.18) 

250(11.97) 

150* (7.18) 

50-100(2.40-4.79) 

80 (3.83) 

40(1.92) 
150* (7.18) 
150* (7.18) 

150* (7.18) 
125* (6.00) 
80* (3.83) 
600* (28.73) 
400 (19.15) 
§ 

150(7.18) 
150 s (7.18) 
100 (4.79) 
150* (7.18) 



Laboratories, scientific 

Laundries 

Libraries, corridors 

Manufacturing, ice 

Morgue 

Office Buildings 

Business machine equipment 

Files (see file room) 
Printing Plants 

Composing rooms 

Linotype rooms 

Paper storage 

Press rooms 
Public rooms 
Railroad tracks 
Ramps 

Driveway (see garages) 

Pedestrian (see sidewalks and corridors in Table 2) 

Seaplane (see hangars) 
Rest rooms 
Rinks 

Ice skating 

Roller skating 
Storage, hay or grain 
Telephone exchange 
Theaters 

Dressing rooms 

Grid-iron floor or fly gallery: 
Grating 

Well beams, 250 lb/ft per pair 
Header beams, 1000 lb/ft 
Pin rail, 250 lb/ft 

Projection room 
Toilet rooms 
Transformer rooms 
Vaults, in offices 



100 (4.79) 
150* (7.18) 
80* (3.83) 
300 (14.36) 
125 (6.00) 

100* (4.79) 



100 (4.79) 
100 (4.79) 

150* (7.18) 
100 (4.79) 



60 (2.87) 

250(11.97) 

100 (4.79) 

300* (14.36) 

150* (7.18) 

40 (1.92) 

60 (2.87) 



100 (4.79) 

60 (2.87) 

200* (9.58) 

250* (11.97) 



Use weight of actual equipment or stored material when greater. 

Plus 150 lb/ft 2 (7.18 kN/m 2 ) for trucks. 

Use American Association of State Highway and Transportation Officials lane loads. Also subject to not less than 100% maximum axle load. 

Paper storage 50 lb/ft (2.40 kN/m 2 ) of clear story height. 

As required by railroad company. 

Accessible ceilings normally are not designed to support persons. The value in this table is intended to account for occasional light storage or 

suspension of items. If it may be necessary to support the weight of maintenance personnel, this shall be provided for. 



Minimum Design Loads for Buildings and Other Structures 



259 









TABLE C4-2 














TYPICAL LSVE LOAD STATSSTSCS 












Survey Load 


Transient Load 


Temporal Constant* 




Mean 
maximum 


Occupancy 
or use 


ffls 
lb/ft 2 (kN/m 2 ) 


lb/ft 2 (kN/m 2 ) 


m t * 
lb/ft 2 (kN/m 2 ) 


lb/ft 2 (kN/m 2 ) 


tst 
(years) 


Vet 
(per year) 


T§ 
(year) 


load* 
ib/ft 2 (kN/m 2 ) 


Office buildings 


















Offices 
Residential 


10.9 (0.52) 


5.9 (0.28) 


8.0 (0.38) 


8.2 (0.39) 


8 


1 


50 


55 (2.63) 


Renter occupied 
Owner occupied 
Hotels 


6,0 (0.29) 
6.0 (0.29) 


2.6(0.12) 
2.6 (0.12) 


6.0 (0.29) 
6.0 (0.29) 


6.6 (0.32) 
6.6 (0.32) 


2 
10 


1 

1 


50 
50 


36 (1.72) 
38 (1.82) 


Guest rooms 
Schools 


4.5 (0.22) 


1.2 (0.06) 


6.0 (0.29) 


5.8 (0.28) 


5 


20 


50 


46 (2.2) 


Classrooms 


12.0 (0.57) 


2.7 (0.13) 


6.9 (0.33) 


3.4 (0.16) 


1 


1 


100 


34 (1.63) 



* For 200-ft 2 (18.58 m 2 ) area, except 1000 ft 2 (92.9 rn 2 )for schools. 
"I" Duration of average sustained load occupancy. 

* Mean rate of occurrence of transient load. 
§ Reference period. 



260 



ASCE 7-02 



SECTION C5-0 

SOIL AND HYDROSTATIC PRESSURE AND FLOOD LOADS 



SECTION C5.1 
PRESSURE ON BASEMENT WALLS 

Table 5-1 includes high earth pressures, 85 pcf (13.36 
kN/m 2 ) or more, to show that certain soils are poor 
backfill material. In addition, when walls are unyielding, 
the earth pressure is increased from active pressure toward 
earth pressure at rest, resulting in 60 pcf (9.43 kN/m 2 ) 
for granular soils and 100 pcf (15.71 kN/m 2 ) for silt 
and clay type soils (see C5-4]). Examples of light floor 
systems supported on shallow basement walls mentioned in 
Table 5-1 are floor systems with wood joists and flooring, 
and cold-formed steel joists without cast-in-place concrete 
floor attached. 

Expansive soils exist in many regions of the United 
States and may cause serious damage to basement walls 
unless special design considerations are provided. Expan- 
sive soils should not be used as backfill because they can 
exert very high pressures against walls. Special soil testing 
is required to determine the magnitude of these pressures. 
It is preferable to excavate expansive soil and backfill with 
nonexpansive freely draining sands or gravels. The exca- 
vated backslope adjacent to the wall should be no steeper 
than 45 degrees from the horizontal in order to minimize 
the transmission of swelling pressure from the expansive 
soil through the new backfill. Other special details are rec- 
ommended, such as a cap of nonpervious soil on top of the 
backfill and provision of foundation drains. Refer to current 
reference books on geotechnical engineering for guidance. 



SECTION C5.2 
UPLIFT ON FLOORS AND FOUNDATIONS 

If expansive soils are present under floors or footings, 
large pressures can be exerted and must be resisted by 
special design. Alternatively, the expansive soil can be 
excavated to a depth of at least 2 ft (0.60 m) and backfilled 
with nonexpansive freely draining sands or gravel. A 
geotechnical engineer should make recommendations in 
these situations. 



SECTION G5.3 
FLOOD LOADS 

This section presents information for the design of buildings 
and other structures in areas prone to flooding. Design 
professionals should be aware that there are important 
differences between flood characteristics, flood loads, and 
flood effects in riverine and coastal areas (e.g., the potential 



for wave effects is much greater in coastal areas; the depth 
and duration of flooding can be much greater in riverine 
areas; the direction of flow in riverine areas tends to be 
more predictable; the nature and amount of flood-borne 
debris varies between riverine and coastal areas). 

Much of the impetus for flood-resistant design has come 
about from the federal government-sponsored initiatives of 
flood-damage mitigation and flood insurance, both through 
the work of the U.S. Army Corps of Engineers and the 
National Flood Insurance Program (NFIP). The NFIP is 
based on an agreement between the federal government 
and participating communities that have been identified 
as being flood prone. The Federal Emergency Manage- 
ment Agency (FEMA) through the Federal Insurance and 
Mitigation Administration (FIMA) makes flood insurance 
available to the residents of communities provided that the 
community adopts and enforces adequate floodplain man- 
agement regulations that meet the minimum requirements. 
Included in the NFIP requirements, found under Title 44 
of the U.S. Code of Federal Regulations [C5-3], are mini- 
mum building design and construction standards for build- 
ings and other structures located in Special Flood Hazard 
Areas (SFHA). 

SFHA are those identified by FEMA as being subject to 
inundation during the 100-year flood. SFHA are shown on 
Flood Insurance Rate Maps (FIRM), which are produced for 
flood-prone communities, SFHA are identified on FIRM'S 
as Zones A, A 1-30, AE, AR, AO, AH, and coastal high 
hazard areas as VI -30, V and VE. The SFHA is the area 
in which communities must enforce NFIP-compliant, flood 
damage-resistant design and construction practices. 

Prior to designing a structure in a flood-prone area, 
design professionals should contact the local building offi- 
cial to determine if the site in question is located in a SFHA 
or other flood-prone area that is regulated under the commu- 
nity's floodplain management regulations. If the proposed 
structure is located within the regulatory floodplain, local 
building officials can explain the regulatory requirements. 

Answers to specific questions on flood-resistant design 
and construction practices may be directed to the Mitigation 
Division of each of FEMA's regional offices. FEMA 
has regional offices that are available to assist design 
professionals. 

C5.3.1 Definitions. Three new concepts were added with 
ASCE 7-98. First, the concept of the Design Flood is 
introduced. The Design Flood will, at a minimum, be 
equivalent to the flood having a 1% chance of being equaled 
or exceeded in any given year (i.e., the Base Flood or 



Minimum Design Loads for Buildings and Other Structures 



261 



100-year flood, which served as the load basis in ASCE 
7-95). In some instances, the Design Flood may exceed the 
Base Flood in elevation or spatial extent — this will occur 
where a community has designated a greater flood (lower 
frequency, higher return period) as the flood to which the 
community will regulate new construction. 

Many communities have elected to regulate to a flood 
standard higher than the minimum requirements of the 
National Flood Insurance Program (NFIP). Those commu- 
nities may do so in a number of ways. For example: a 
community may require new construction to be elevated a 
specific vertical distance above the Base Flood Elevation 
(this is referred to as freeboard); a community may select 
a lower frequency flood as its regulatory flood; a commu- 
nity may conduct hydrologic and hydraulic studies, upon 
which Flood Hazard Maps are based, in a manner different 
than the Flood Insurance Study prepared by the NFIP (the 
community may complete flood hazard studies based upon 
development conditions at build-out, rather than following 
the NFIP procedure, which uses conditions in existence at 
the time the studies are completed; the community may 
include watersheds smaller than 1 mi 2 in size in its analysis, 
rather than following the NFIP procedure, which neglects 
watersheds smaller than 1 mi 2 ). 

Use of the Design Flood concept will ensure that the 
requirements of this Standard are not less restrictive than 
a community's requirements where that community has 
elected to exceed minimum NFIP requirements. In instances 
where a community has adopted the NFIP minimum 
requirements, the Design Flood described in this Standard 
will default to the Base Flood. 

Second, this Standard also uses the terms Flood Hazard 
Area and Flood Hazard Map to correspond to and show 
the areas affected by the Design Flood. Again, in instances 
where a community has adopted the minimum requirements 
of the NFIP, the Flood Hazard Area defaults to the NFIP's 
Special Flood Hazard Area and the Flood Hazard Map 
defaults to the Flood Insurance Rate Map. 

Third, the concept of a Coastal A Zone is used to 
facilitate application of load combinations contained in 
Section 2. Coastal A Zones lie landward of Y Zones, or 
landward of an open coast shoreline where V Zones have 
not been mapped (e.g., the shorelines of the Great Lakes), 
Coastal A Zones are subject to the effects of waves, high- 
velocity flows, and erosion, although not to the extent that 
V Zones are. Like V Zones, flood forces in coastal A Zones 
will be highly correlated with coastal winds or coastal 
seismic activity. 

C5.3.2 Design Requirements. Sections 5.3.4 (dealing with 
A-Zone design and construction) and 5.3.5 (dealing with 
Y-Zone design and construction) of ASCE 7-98 have been 
deleted. These sections summarized basic principles of flood- 
resistant design and construction (building elevation, anchor- 
age, foundation, below-DFE enclosures, breakaway walls, 
etc.). Some of the information contained in these deleted 



sections has been included in Section 5.3 of ASCE 7-02, and 
the design professional is also referred to SEI/ASCE 24-98 
{Standard for Flood Resistant Design and Construction) for 
specific guidance. 

C5.3.2.1 Design Loads. Wind loads and flood loads may 
act simultaneously at coastlines, particularly during hurri- 
canes and coastal storms. This may also be true during 
severe storms at the shorelines of large lakes, and during 
riverine flooding of long duration. 

C5.3.2.2 Erosion and Scour. The term "erosion" indi- 
cates a lowering of the ground surface in response to a 
flood event, or in response to the gradual recession of a 
shoreline. The term "scour" indicates a localized lowering 
of the ground surface during a flood due to the interaction 
of currents and/or waves with a structural element. Erosion 
and scour can affect the stability of foundations, and can 
increase the local flood depth and flood loads acting on 
buildings and other structures. For these reasons, erosion 
and scour should be considered during load calculations 
and the design process. Design professionals often increase 
the depth of foundation embedment to mitigate the effects 
of erosion and scour, and often site buildings away from 
receding shorelines (building set-backs). 

C5.3.3.6 Loads on Breakaway Walls. Floodplain man- 
agement regulations require buildings in coastal high hazard 
areas to be elevated to or above the design flood eleva- 
tion by a pile or column foundation. Space below the DFE 
must be free of obstructions in order to allow the free pas- 
sage of waves and high-velocity waters beneath the building 
[C5-6]. Floodplain management regulations typically allow 
space below the DFE to be enclosed by insect screen- 
ing, open lattice, or breakaway walls. Local exceptions are 
made in certain instances for shear walls, firewalls, eleva- 
tor shafts, and stairwells — check with the authority having 
jurisdiction for specific requirements related to obstructions, 
enclosures, and breakaway walls. 

Where breakaway walls are used, they must meet the 
prescriptive requirements of NFIP regulations or be cer- 
tified by a registered professional engineer or architect 
as having been designed to meet the NFIP performance 
requirements. The prescriptive requirements call for break- 
away wall designs which are intended to collapse at loads 
not less than 10 psf (0.48 kN/m 2 ) and not more than 
20 psf (0.96 kN/m 2 ). Inasmuch as wind or earthquake loads 
often exceed 20 psf (0.96 kN/m 2 ), breakaway walls may be 
designed for a higher load, provided the designer certifies 
that the walls have been designed to break away before 
base flood conditions are reached without damaging the ele- 
vated building or its foundation. A recent reference [C5-7] 
provides guidance on how to meet the performance require- 
ments for certification. 



262 



ASCE 7-02 



C5.3.3.1 Load Basis. Water loads are the loads or pres- 
sures on surfaces of buildings and structures caused and 
induced by the presence of floodwaters. These loads are 
of two basic types: hydrostatic and hydrodynamic. Impact 
loads result from objects transported by floodwaters striking 
against buildings and structures or part thereof. Wave loads 
can be considered a special type of hydrodynamic load. 

C5.3.3.2 Hydrostatic Loads. Hydrostatic loads are those 
caused by water either above or below the ground surface, 
free or confined, which is either stagnant or moves at 
velocities less than 5 ft/sec (1.52 m/s). These loads are 
equal to the product of the water pressure multiplied by 
the surface area on which the pressure acts. 

Hydrostatic pressure at any point is equal in all directions 
and always acts perpendicular to the surface on which 
it is applied. Hydrostatic loads can be subdivided into 
vertical downward loads, lateral loads, and vertical upward 
loads (uplift or buoyancy). Hydrostatic loads acting on 
inclined, rounded, or irregular surfaces may be resolved 
into vertical downward or upward loads and lateral loads 
based on the geometry of the surfaces and the distribution 
of hydrostatic pressure. 

C5.3.3.3 Hydrodynamic Loads. Hydrodynamic loads are 
those loads induced by the flow of water moving at 
moderate-to-high velocity above the ground level. They are 
usually lateral loads caused by the impact of the moving 
mass of water and the drag forces as the water flows around 
the obstruction. Hydrodynamic loads are computed by rec- 
ognized engineering methods. In the coastal high hazard 
area, the loads from high- velocity currents due to storm 
surge and overtopping are of particular importance. Refer- 
ence [C5-1] is one source of design information regarding 
hydrodynamic loadings. 

Note that accurate estimates of flow velocities during 
flood conditions are very difficult to make, both in river- 
ine and coastal flood events. Potential sources of infor- 
mation regarding velocities of floodwaters include local, 
state, and federal government agencies and consulting engi- 
neers specializing in coastal engineering, stream hydrology, 
or hydraulics. 

As interim guidance for coastal areas, see Refer- 
ence [C5-8], which gives a likely range of flood veloci- 
ties as: 

V=d s /0 sec) (Eq. C5-1) 



to 



where 



V = (gd s ) 



0.5 



(Eq. C5-2) 



V = average velocity of water in ft/sec (m/s) 
d s — local Stillwater depth in ft (m) 
g — acceleration due to gravity, 32.2 ft/sec (9.81 m/s 2 ) 



Selection of the correct value of "a" in Eq. 5-1 will 
depend upon the shape and roughness of the object exposed 
to flood flow, as well as the flow condition itself. As a gen- 
eral rule, the smoother and more streamlined the object, the 
lower the drag coefficient (shape factor). Drag coefficients 
for elements common in buildings and structures (round or 
square piles, columns, and rectangular shapes) will range 
from approximately 1.0 to 2.0, depending upon flow con- 
ditions. However, given the uncertainty surrounding flow 
conditions at a particular site, ASCE 7-02 recommends a 
minimum value of 1.25 be used. Fluid mechanics texts 
should be consulted for more information on when to apply 
drag coefficients above 1.25. 

C5.3.3.4 Wave Loads. The magnitude of wave forces 
(lbs/ft 2 )(kN/m 2 ) acting against buildings or other structures 
can be 10 or more times higher than wind forces and other 
forces under design conditions. Thus, it should be readily 
apparent that elevating above the wave crest elevation is 
crucial to the survival of buildings and other structures. 
Even elevated structures, however, must be designed for 
large wave forces that can act over a relatively small surface 
area of the foundation and supporting structure. 

Wave load calculation procedures in Section 5.3.3.4 are 
taken from References [C5-1] and [C5-5], The analytical 
procedures described by Eqs. 5-2 through 5-9 should be 
used to calculate wave heights and wave loads unless more 
advanced numerical or laboratory procedures permitted by 
this Standard are used. 

Wave load calculations using the analytical procedures 
described in this Standard all depend upon the initial 
computation of the wave height, which is determined 
using Eqs. 5-2 and 5-3. These equations result from the 
assumptions that the waves are depth-limited, and that 
waves propagating into shallow water break when the wave 
height equals 78% of the local Stillwater depth and that 
70% of the wave height lies above the local Stillwater level. 
These assumptions are identical to those used by FEMA in 
its mapping of coastal flood hazard areas on FIRMs. 

Designers should be aware that wave heights at a 
particular site can be less than depth-limited values in some 
cases (e.g., when the wind speed, wind duration, or fetch 
is insufficient to generate waves large enough to be limited 
in size by water depth, or when nearby objects dissipate 
wave energy and reduce wave heights). If conditions during 
the design flood yield wave heights at a site less than 
depth-limited heights, Eq. 5-2 may overestimate the wave 
height and Eq. 5-3 may underestimate the Stillwater depth. 
Also, Eqs. 5-4 through 5-7 may overstate wave pressures 
and forces when wave heights are less than depth-limited 
heights. More advanced numerical or laboratory procedures 
permitted by this section may be used in such cases, in lieu 
of Eqs. 5-2 through 5-7. 

It should be pointed out that present NFIP mapping 
procedures distinguish between A Zones and V Zones 
by the wave heights expected in each zone. Generally 



Minimum Design Loads for Buildings and Other Structures 



263 



speaking, A Zones are designated where wave heights 
less than 3 ft (0.91 m) in height are expected; V Zones 
are designated where wave heights equal to or greater 
than 3 ft (0.91 m) are expected. Designers should proceed 
cautiously, however. Large wave forces can be generated 
in some A Zones, and wave force calculations should not 
be restricted to V Zones. Present NFIP mapping procedures 
do not designate V Zones in all areas where wave heights 
greater than 3 ft (0.91 m) can occur during base flood 
conditions. Rather than rely exclusively on flood hazard 
maps, designers should investigate historical flood damages 
near a site to determine whether or not wave forces can be 
significant. 

C5.3.3.4.2 Breaking Wave Loads on Vertical Wails. 
Equations used to calculate breaking wave loads on verti- 
cal walls contain a coefficient, C p , Reference [C5-5] pro- 
vides recommended values of the coefficient as a function 
of probability of exceedance. The probabilities given by Ref- 
erence [C5-5] are not annual probabilities of exceedance, but 
probabilities associated with a distribution of breaking wave 
pressures measured during laboratory wave tank tests. Note 
that the distribution is independent of water depth. Thus, for 
any water depth, breaking wave pressures can be expected 
to follow the distribution described by the probabilities of 
exceedance in Table 5-2. 

This Standard assigns values for C p according to the 
building category with the most important buildings hav- 
ing the largest values of C p . Category 11 buildings are 
assigned a value of C p corresponding to a 1% probabil- 
ity of exceedance, which is consistent with wave analysis 
procedures used by FEMA in mapping coastal flood hazard 
areas and in establishing minimum floor elevations. Cate- 
gory I buildings are assigned a value of C p corresponding 
to a 50% probability of exceedance, but designers may 
wish to choose a higher value of C p . Category III build- 
ings are assigned a value of C p corresponding to a 0.2% 
probability of exceedance, while Category IV buildings are 
assigned a value of C p corresponding to a 0.1 % probability 
of exceedance. 

Breaking wave loads on vertical walls reach a maximum 
when the waves are normally incident (direction of wave 
approach perpendicular to the face of the wall; wave 
crests are parallel to the face of the wall). As guidance 
for designers of coastal buildings or other structures on 
normally dry land (i.e., flooded only during coastal storm 
or flood events), it can be assumed that the direction 
of wave approach will be approximately perpendicular to 
the shoreline. Therefore, the direction of wave approach 
relative to a vertical wall will depend upon the orientation of 
the wall relative to the shoreline. Section 5.3.3.4.4 provides 
a method for reducing breaking wave loads on vertical walls 
for waves not normally incident. 

C5.3.3.5 Impact Loads. Impact loads are those that result 
from logs, ice floes, and other objects striking buildings, 



structures, or parts thereof. Reference [C5-2] divides impact 
loads into three categories: (1) normal impact loads, which 
result from the isolated impacts of normally encountered 
objects; (2) special impact loads that result from large 
objects, such as broken up ice floats and accumulations 
of debris, either striking or resting against a building, 
structure, or parts thereof; and (3) extreme impact loads 
that result from very large objects such as boats, barges, 
or collapsed buildings striking the building, structure, or 
component under consideration. Design for extreme impact 
loads is not practical for most buildings and structures. 
However, in cases where there is a high probability that a 
Category III or IV structure (see Table 1 - 1 ) will be exposed 
to extreme impact loads during the design flood, and where 
the resulting damages will be very severe, consideration 
of extreme impact loads may be justified. Unlike extreme 
impact loads, design for special and normal impact loads is 
practical for most buildings and structures. 

The recommended method for calculating normal impact 
loads has been modified with ASCE 7-02. Previous editions 
of ASCE 7 used a procedure contained in Reference [C5-2] 
(the procedure, which had been unchanged since at least 
1972, relied on an impulse-momentum approach with a 
1000 lb (4.5 kN) object striking the structure at the velocity 
of the floodwater and coming to rest in 1.0 sec). Recent 
work [C5-9 and C5-1.0] has been conducted to evaluate this 
procedure, through a literature review and laboratory tests. 
The literature review considered riverine and coastal debris, 
ice floes and impacts, ship berthing and impact forces, and 
various methods for calculating debris loads (e.g., impulse- 
momentum, work-energy). The laboratory tests included log 
sizes ranging from 380 lbs (1.7 kN) to 730 lbs (3.3 kN) 
travelling at up to 4 ft/sec (1.2 m/s). 

References [C5-9 and C5-10] conclude: (1) an impulse- 
momentum approach is appropriate; (2) the 1000 lb 
(4.5 kN) object is reasonable, although geographic and local 
conditions may affect the debris object size and weight; 
(3) the 1.0 second impact duration is not supported by the 
literature or by laboratory tests — a duration of impact of 
0.03 seconds should be used instead; (4) a half-sine curve 
represents the applied load and resulting displacement well; 
and (5) setting the debris velocity equivalent to the flood 
velocity is reasonable for all but the largest objects in 
shallow water or obstructed conditions. 

Given the short-duration, impulsive loads generated by 
flood-borne debris, a dynamic analysis of the affected 
building or structure may be appropriate. In some cases 
(e.g., when the natural period of the building is much 
greater than 0.03 seconds), design professionals may wish 
to treat the impact load as a static load applied to the 
building or structure (this approach is similar to that used by 
some following the procedure contained in Section C5.3.3.5 
of ASCE 7-98). 

In either type of analysis — dynamic or static — 
Eq. C5-3 provides a rational approach for calculating the 



264 



ASCE 7-02 



magnitude of the impact load. 

7ZWV b CiC C D C B Rn 



F = 



2s At 



(Eq. C5-3) 



where 



F = impact force, in lbs (N) 
W = debris weight in lbs (N) 
V h = velocity of object (assume equal to velocity of 

water, V) in ft/sec (m/s) 
g = acceleration due to gravity, = 32.2 ft/sec 2 

(9.81 m/s 2 ) 
A^ — impact duration (time to reduce object velocity to 

zero), in seconds. 
C[ = importance coefficient (see Table C5-3) 
Co = orientation coefficient, = 0.8. 
C D = depth coefficient (see Table C5-4, Figure C5-3) 
C B = blockage coefficient (see Table C5-5, 

Figure C5-4) 
R max = maximum response ratio for impulsive load (see 

Table C5-6) 

The form of Eq. C5-3 and the parameters and coeffi- 
cients are discussed below: 

Basic Equation. The equation is similar to the 
equation used in ASCE 7-98, except for the Till fac- 
tor (which results from the half- sine form of the 
applied impulse load) and the coefficients C/, Co, 
Co, Cb, and R max - With the coefficients set equal 
to 1.0, the equation reduces to F — nWVb/2g&t, 
and calculates the maximum static load from a head- 
on impact of a debris object. The coefficients have 
been added to allow design professionals to "cali- 
brate" the resulting force to local flood, debris, and 
building characteristics. The approach is similar to 
that employed by ASCE 7 in calculating wind, seis- 
mic, and other loads — a scientifically based equation 
is used to match the physics, and the results are 
modified by coefficients to calculate realistic load 
magnitudes. However, unlike wind, seismic, and other 
loads the body of work associated with flood-borne 
debris impact loads does not yet account for the prob- 
ability of impact. 

Debris Object Weight A 1000-lb object can be con- 
sidered a reasonable average for flood-borne debris 
(no change from ASCE 7-98). This represents a rea- 
sonable weight for trees, logs, and other large woody 
debris, which is the most common form of damag- 
ing debris nationwide. This weight corresponds to a 
log approximately 30 ft (9.1 m) long and just under 
1 ft (0.3 m) in diameter. The 1000-lb object also 
represents a reasonable weight for other types of 
debris ranging from small ice floes, to boulders, to 
man-made objects. 



However, design professionals may wish to con- 
sider regional or local conditions before the final 
debris weight is selected. The following text provides 
additional guidance. In riverine floodplains, large 
woody debris (trees and logs) predominates, with 
weights typically ranging from 1000 lbs (4.5 kN) to 
2000 lbs (9.0 kN). In the Pacific Northwest, larger 
tree and log sizes suggest a typical 4000 lb (18.0 kN) 
debris weight. Debris weights in riverine areas sub- 
ject to floating ice typically range from 1000 lbs 
(4.5 kN) to 4000 lbs (18.0 kN). In arid or semi- 
arid regions, typical woody debris may be less than 
1000 lbs (4.5 kN). In alluvial fan areas, non- woody 
debris (stones and boulders) may present a much 
greater debris hazard. 

Debris weights in coastal areas generally fall into 
three classes: in the Pacific Northwest, a 4000 lb 
(18.0 kN) debris weight due to large trees and logs 
can be considered typical; in other coastal areas 
where piers and large pilings are available locally, 
debris weights may range from 1000 lbs (4.5 kN) to 
2000 lbs (9.0 kN); in other coastal areas where large 
logs and pilings are not expected, debris will likely 
be derived from failed decks, steps, and building 
components, and will likely average less than 500 lbs 
(2.3 kN) in weight. 



Debris Velocity. The velocity that a piece of debris 
strikes a building or structure will depend upon 
the nature of the debris and the velocity of the 
floodwaters. Small pieces of floating debris, which 
are unlikely to cause damage to buildings or other 
structures, will typically travel at the velocity of 
the floodwaters, in both riverine and coastal flood 
situations. However, large debris, such as trees, logs, 
pier pilings, and other large debris capable of causing 
damage, will likely travel at something less than the 
velocity of the floodwaters. This reduced velocity of 
large debris objects is due in large part to debris 
dragging along the bottom and/or being slowed by 
prior collisions. Large riverine debris travelling along 
the floodway (the deepest part of the channel that 
conducts the majority of the flood flow) is most 
likely to travel at speeds approaching that of the 
floodwaters. Large riverine debris travelling in the 
floodplain (the shallower area outside the floodway) 
is more likely to be travelling at speeds less than that 
of the floodwaters, for those reasons stated above. 
Large coastal debris is also likely to be travelling at 
speeds less than that of the floodwaters. Eq. C5-2 
should be used with the debris velocity equal to 
the flow velocity, since the equation allows for 
reductions in debris velocities through application of 
a depth coefficient, Co and an upstream blockage 
coefficient, C B . 



Minimum Design Loads for Buildings and Other Structures 



265 



Duration of Impact. A detailed review of the 
available literature [C5-9], supplemented by labo- 
ratory testing, concluded the previously suggested 
1.0 second duration of impact is much too long and 
is not realistic. Laboratory tests showed that mea- 
sured impact durations (from initial impact to time of 
maximum force At) varied from 0.01 sec to 0.05 sec 
[C5-9]. Results for one test, for example, produced a 
maximum impact load of 8300 lbs (37,000 N) for a 
log weighing 730 lbs (3250 N), moving at 4 ft/sec, 
and impacting with a duration of 0.016 sec. Over 
all the test conditions, the impact duration averaged 
about 0.026 sec. The recommended value for use in 
Eq. C5-2 is, therefore, 0.03 sec. 

Coefficients Q 9 Co 9 Co, and C#* The coefficients 
are based in part on the results of laboratory testing 
and in part on engineering judgement. The values 
of the coefficients should be considered interim until 
more experience is gained with them. 

The Importance Coefficient. Cj is generally used 
to adjust design loads for the structure category 
and hazard to human life following ASCE-7-98 
convention in Table 1-1. Recommended values given 
in Table C5-3 are based on a probability distribution 
of impact loads obtained from laboratory tests in 
Reference [C5-10]. 

The Orientation Coefficient Co is used to reduce 
the load calculated by Eq. C5-3 for impacts that are 
oblique, not head-on. During laboratory tests [C5-10] 
it was observed that while some debris impacts 
occurred as direct or head-on impacts that produced 
maximum impact loads, most impacts occurred as 
eccentric or oblique impacts with reduced values of 
the impact force. Based on these measurements, an 
orientation coefficient of C =0.8 has been adopted 
to reflect the general load reduction observed due to 
oblique impacts. 

The Depth Coefficient. Co is used to account for 
reduced debris velocity in shallow water due to debris 
dragging along the bottom. Recommended values of 
this coefficient are based on typical diameters of 
logs and trees, or on the anticipated diameter of the 
root mass from drifting trees that are likely to be 
encountered in a flood hazard zone. Reference [C5-9] 
suggests that trees with typical root mass diameters 
will drag the bottom in depths of less than 5 ft, 
while most logs of concern will drag the bottom in 
depths of less than 1 ft. The recommended values 
for the depth coefficient are given in Table C5-4 
and Figure C5-3. No test data are available to fully 



validate the recommended values of this coefficient. 
When better data are available, designers should use 
them in lieu of the values contained in Table C5-4 
and Figure C5-3. 

The Blockage Coefficient. Cg is used to account 
for the reductions in debris velocities expected due 
to screening and sheltering provided by trees or 
other structures within about 10 log-lengths (300 ft) 
upstream from the building or structure of interest. 
Reference [C5-9] quotes other studies in which dense 
trees have been shown to act as a screen to remove 
debris and shelter downstream structures. The effec- 
tiveness of the screening depends primarily on the 
spacing of the upstream obstructions relative to the 
design log length of interest. For a 1000-lb log, hav- 
ing a length of about 30 ft, it is therefore assumed that 
any blockage narrower than 30 ft would trap some or 
all of the transported debris. Likewise, typical root 
mass diameters are on the order of 3 to 5 ft, and it is 
therefore assumed that blockages of this width would 
fully trap any trees or long logs. Recommended values 
for the blockage coefficient are given in Table C5-5 
and Figure C5-4 based on interpolation between these 
limits. No test data are available to fully validate the 
recommended values of this coefficient. 

The Maximum Response Ratio. R max is used to 
increase or decrease the computed load, depending 
on the degree of compliance of the building or 
building component being struck by debris. Impact 
loads are impulsive in nature with the force rapidly 
increasing from zero to the maximum value in time 
At, then decreasing to zero as debris rebounds from 
structure. The actual load experienced by the structure 
or component will depend on the ratio of the impact 
duration At relative to the natural period of the 
structure or component, T n . Stiff or rigid buildings 
and structures with natural periods similar to the 
impact duration will see an amplification of the 
impact load. More flexible buildings and structures 
with natural periods greater than approximately 4 
times the impact duration will see a reduction of 
the impact load. Likewise, stiff or rigid components 
will see an amplification of the impact load; more 
flexible components will see a reduction of the impact 
load. Successful use of Eq. C5-3, then, depends on 
estimation of the natural period of the building 
or component being struck by flood-borne debris. 
Calculating the natural period can be carried out 
using established methods that take building mass, 
stiffness, and configuration into account. One useful 
reference is Appendix C of ANSI/ACI 349 [C5-12]. 
Design professionals are also referred to Section 9 of 
ASCE 7-02 for additional information. 



266 



ASCE 7-02 



Natural periods of buildings generally vary from 
approximately 0.05 sec to several seconds (for high- 
rise, moment frame structures). For flood-borne debris 
impact loads with a duration of 0.03 sec, the critical 
period (above which loads are reduced) is approx- 
imately 0.11 sec (see Table C5-6). Buildings and 
structures with natural periods above approximately 
0.1 1 sec will see a reduction in the debris impact load, 
while those with natural periods below approximately 
0.1 1 sec will, see an increase. Recent shake table tests 
of conventional, one- to two-story wood-frame build- 
ings have shown natural periods of ranging from 
approximately 0.14 sec (7 Hz) to 0.33 sec (3 Hz), 
averaging approximately 0.20 sec (5 Hz). Elevating 
these types of structures for flood-resistant design 
purposes will act to increase these natural periods. 
For the purposes of flood-borne debris impact load 
calculations, a natural period of 0.5 to 1.0 sec is rec- 
ommended for one- to three-story buildings elevated 
on timber piles. For 1- to 3-story buildings elevated on 
masonry columns, a similar range of natural periods 
is recommended. For 1- to 3-story buildings elevated 
on concrete piles or columns, a natural period of 0.2 
to 0.5 sec is recommended. Design professionals are 
referred to Section 9.5.5.3 of ASCE 7-02 (or 9.5.3.3 
of ASCE 7-98) where an approximate natural period 
for 1- to 12-story buildings (story height equal to 
or greater than 10 ft [3 m]), with concrete and steel 
moment-resisting frames can be approximated as 0.1 
times the number of stories. 



Special Impact Loads. Reference [C5-2] states that, 
absent a detailed analysis, special impact loads can be 
estimated as a uniform load of 100 lbs/ft (1.48 kN/m), 
acting over a 1 ft (0.31 m) high horizontal strip 
at the design flood elevation or lower. However, 
Reference [C5-9] suggests that this load may be too 
small for some large accumulations of debris, and 
suggests an alternative approach involving application 
of the standard drag force expression 



F = {\/2)C D pAV 1 



where 



This expression produces loads similar to the 
100 lb/ft guidance from Reference [C5-2] when the 
debris depth is assumed to be 1 ft and when the 
velocity of the floodwater is 10 ft/sec. Other guid- 
ance from References [C5-9] and [C5-10] suggest 
that the depth of debris accumulation is often much 
greater than 1 ft, and is only limited by the water 
depth at the structure. Observations of debris accu- 
mulations at bridge piers listed in these references 
show typical depths of 5 to 10 ft, with horizon- 
tal widths spanning between adjacent bridge piers 
whenever the spacing of the piers is less than the 
typical log length. If debris accumulation is of con- 
cern, the design professional should specify the pro- 
jected area of the debris accumulation based on local 
observations and experience, and apply the above 
equation to predict the debris load on buildings or 
other structures. 



[C5-1] 

[C5-2] 

[C5-3] 

[C5-4] 
[C5-5] 



[C5-6] 



(Eq. C5-4) [ C5 - ? ] 



F — drag force due to debris accumulation, in 

lbs (N) [C5-8] 

V = flow velocity upstream of debris 
accumulation, in ft/sec (m/s) 

A = projected area of the debris accumulation into [C5-9] 

the flow, approximated by depth of 
accumulation times width of accumulation 
perpendicular to flow, in ft 2 (m 2 ) [C5-10] 

p — density of water in slugs/ft 3 (kg/m 3 ) 
C D — drag coefficient = 1 



REFERENCES 

U.S. Army Corps of Engineers, Coastal Engineer- 
ing Research Center, Waterways Experiment Sta- 
tion, Shore Protection Manual, 4th Ed., 1984. 
U.S. Army Corps of Engineers, Office of the 
Chief of Engineers, Flood Proofing Regulations, 
EP 1165-2-314, December 1995. 
Federal Emergency Management Agency, National 
Flood Insurance Program, 44 CFR Ch. 1 Parts 59 
and 60, (10-1-99 Edition), 1990. 
Terzaghi, K. and Peck, R.B., Soil Mechanics in 
Engineering Practice, Wiley, 2nd Ed., 1967. 
Walton, T.L., Jr., J.P. Ahrens, C.L. Truitt, and 
R.G. Dean, Criteria for Evaluating Coastal Flood 
Protection Structures, Technical Report CERC 89- 
15, U.S. Army Corps of Engineers, Waterways 
Experiment Station, 1989. 

Federal Emergency Management Agency, Free-of- 
Obstruction Requirements for Buildings Located 
in Coastal High Hazard Areas in accordance with 
the National Flood Insurance Program, Technical 
Bulletin 5-93. Mitigation Directorate, 1993. 
Federal Emergency Management Agency, Design 
and Construction Guidance for Breakaway Walls 
Below Elevated Coastal Buildings in accordance 
with the National Flood Insurance Program, Tech- 
nical Bulletin 9-99. Mitigation Directorate, 1999. 
Federal Emergency Management Agency, Revised 
Coastal Construction Manual, FEMA-55. Mitiga- 
tion Directorate, 2000. 

Kriebel, D.L., Buss, L., and Rogers, S. Impact 
Loads from Flood-Borne Debris. Report to the 
American Society of Civil Engineers, 2000. 
Haehnel, R. and Daly, S., "Debris Impact Tests," 
Report prepared for the American Society of 
Civil Engineers by the U.S. Army Cold Regions 



Minimum Design Loads for Buildings and Other Structures 



267 



Research and Engineering Laboratory, Hanover, 
NHL, 2001. 

[C5-11] dough, R.W. and Penzien, J., Dynamics of Struc- 
tures, 2nd Ed. McGraw-Hill, New York, 1975. 

[C5-12] American Concrete Institute. ANSI/ACI 349, Code 
Requirements for Nuclear Safety Related Concrete 
Structures, 1985. 



I 










0.8™ 


















c 

CD 

1 0.6- 

CD 
O 
CJ> 

£ 0.4- 

CD 

Q 

0.2- 














































y\ [ j I [ i 




0- 






£ — \ j 4 1 • 1 j 


\ 



2 3 4 

Water depth (ft) 

FIGURE C5-3 
DEPTH COEFFICIENT, C D 



1 








0.8- 

c 

CD n 














% 0.6- 

o 

o 










i i : i 




CD 

5 0.4- 

u 

o 




i ! : ! 






i i ; i 




CD 

0.2- 














0- 


£. ( ; , 


i i 1 1 1 





10 20 30 40 

Flow channel width upstream (ft) 



50 



TABLE C5-3 

VALUES OF 

IMPORTANCE 

COEFFICIENT, C, 



Building Category 


o t 


I 


0.6 


II 


1.0 


III 


1.2 


IV 


1.3 



TABLE C5-4 
VALUES OF DEPTH COEFFICIENT, C D 



Building Location in Flood Hazard Zone and Water Depth 


D 


Floodway or V Zone 


1.0 


A Zone, Stillwater depth > 5 f t 


1.0 


A Zone, Stillwater depth = 4 f t 


0.75 


A Zone, Stillwater depth = 3 ft 


0.5 


A Zone, Stillwater depth = 2 f t 


0.25 


Any flood zone, Stillwater depth < 1 ft 


0.0 



TABLE C5-5 
VALUES OF BLOCKAGE COEFFICIENT, C B 



Degree of screening or sheltering within 100 ft upstream 


c B 


No upstream screening, flow path wider than 30 ft 


1.0 


Limited upstream screening, flow path 20 ft wide 


0.6 


Moderate upstream screening, flow path 10 ft wide 


0.2 


Dense upstream screening, flow path <5 ft wide 


0.0 



FIGURE C5-4 
BLOCKAGE COEFFICIENT, C e 



268 



ASCE 7-02 



TABLE C5-6 

VALUES OF RESPONSE RATIO FOR IMPULSIVE 

LOADS, R max (ADAPTED FROM [C5-11, 

FIGURE 5-6]) 



Ratio of Impact Duration to 
Natural Period of Structure 


Rmax (Response Ratio for Half-Sine 
Wave Impulsive Load) 


0,00 


0.0 


0.10 


0.4 


0.20 


0.8 


0.30 


1.1 


0.40 


1.4 


0.50 


1.5 


0.60 


1.7 


0.70 


1.8 


0.80 


1.8 


0.90 


1.8 


1.00 


1.7 


1.10 


1.7 


1.20 


1.6 


1.30 


1.6 


>1.40 


1.5 



Minimum Design Loads for Buildings and Other Structures 



269 



SECTION C6.0 

WIND LOADS 



SECTION C6.1 
GENERAL 

The ASCE 7-02 version of the wind load standard provides 
three methods from which the designer can choose. An 
expanded "simplified method" (Method 1) for which the 
designer can select wind pressures directly without any 
calculation when the building meets all the requirements 
for application of the procedure; and two other methods 
(Analytical Method and Wind Tunnel Procedure), which 
are essentially the same methods as previously given in the 
standard except for changes that are noted. 

Temporary bracing should be provided to resist wind 
loading on structural components and structural assem- 
blages during erection and construction phases. 



SECTION C6.2 
DEFINITIONS 

Several important definitions given in the standard are 
discussed further below. These terms are used throughout 
the standard and are provided to clarify application of the 
standard provisions. 

MAIN WIND FORCE-RESISTING SYSTEM. Can con- 
sist of a structural frame or an assemblage of structural 
elements that work together to transfer wind loads acting 
on the entire structure to the ground. Structural elements 
such as cross-bracing, shear walls, roof trusses, and roof 
diaphragms are part of the main wind force-resisting system 
when they assist in transferring overall loads [C6-87]. 

BUILDING, ENCLOSED, OPEN, PARTIALLY EN- 
CLOSED. These definitions relate to the proper selection 
of internal pressure coefficients, GC pi . Building, open 
and Building, partially enclosed are specifically defined. 
All other buildings are considered to be enclosed by 
definition, although there may be large openings in two 
or more walls. An example of this is a parking garage 
through which the wind can pass. The internal pressure 
coefficient for such a building would be ±0.18, and the 
internal pressures would act on the solid areas of the walls 
and roof. 

COMPONENTS AND CLADDING. Components re- 
ceive wind loads directly or from cladding and transfer 
the load to the main wind force-resisting system. Cladding 
receives wind loads directly. Examples of components 



include fasteners, purlins, girts, studs, roof decking, and 
roof trusses. Components can be part of the main wind 
force-resisting system when they act as shear walls or roof 
diaphragms, but they may also be loaded as individual 
components. The engineer needs to use appropriate load- 
ings for design of components, which may require certain 
components to be designed for more than one type of load- 
ing (e.g., long span roof trusses should be designed for 
loads associated with main wind force-resisting systems, 
and individual members of trusses should also be designed 
for component and cladding loads [C6-87]). Examples of 
cladding include wall coverings, curtain walls, roof cover- 
ings, exterior windows (fixed and operable) and doors, and 
overhead doors. 

Effective wind area is the area of the building surface 
used to determine GC P . This area does not necessarily 
correspond to the area of the building surface contributing 
to the force being considered. Two cases arise. In the usual 
case, the effective wind area does correspond to the area 
tributary to the force component being considered. For 
example, for a cladding panel, the effective wind area may 
be equal to the total area of the panel; for a cladding 
fastener, the effective wind area is the area of cladding 
secured by a single fastener. A mulllon may receive wind 
from several cladding panels; in this case, the effective 
wind area is the area associated with the wind load that 
is transferred to the mullion. 

The second case arises where components such as 
roofing panels, wall studs, or roof trusses are spaced closely 
together; the area served by the component may become 
long and narrow. To better approximate the actual load 
distribution in such cases, the width of the effective wind 
area used to evaluate GC P need not be taken as less than 
one third the length of the area. This increase in effective 
wind area has the effect of reducing the average wind 
pressure acting on the component. Note, however, that this 
effective wind area should only be used in determining 
the GC P in Figures 6-5 through 6-8. The induced wind 
load should be applied over the actual area tributary to the 
component being considered. 

For membrane roof systems, the effective wind area is 
the area of an insulation board (or deck panel if insulation is 
not used) if the boards are fully adhered (or the membrane 
is adhered directly to the deck). If the insulation boards or 
membrane are mechanically attached or partially adhered, 
the effective wind area is the area of the board or membrane 
secured by a single fastener or individual spot or row 
of adhesive. 



Minimum Design Loads for Buildings and Other Structures 



271 



FLEXIBLE BUILDINGS AND OTHER STRUCTU- 
RES. A building or other structure is considered flexi- 
ble if it contains a significant dynamic resonant response. 
Resonant response depends on the gust structure con- 
tained in the approaching wind, on wind loading pressures 
generated by the wind flow about the building, and on 
the dynamic properties of the building or structure. Gust 
energy in the wind is smaller at frequencies above about 
1 Hz; therefore the resonant response of most buildings 
and structures with lowest natural frequency above 1 Hz 
will be sufficiently small that resonant response can often 
be ignored. When buildings or other structures have a 
height exceeding four times the least horizontal dimen- 
sion or when there is reason to believe that the natu- 
ral frequency is less than 1 Hz (natural period greater 
than 1 second), natural frequency for it should be inves- 
tigated. A useful calculation procedure for natural fre- 
quency or period for various building types is contained 
in Section 9. 

REGULAR SHAPED BUILDINGS AND OTHER 
STRUCTURES. Defining the limits of applicability of 
the analytical procedures within the standard is a diffi- 
cult process, requiring a balance between the practical 
need to use the provisions past the range for which data 
has been obtained and restricting use of the provisions 
past the range of realistic application. Wind load provi- 
sions are based primarily on wind-tunnel tests on shapes 
shown in Figures 6-6 through 6-17. Extensive wind-tunnel 
tests on actual structures under design show that rela- 
tively large changes from these shapes can, in many cases, 
have minor changes in wind load, while in other cases 
seemingly small changes can have relatively large effects, 
particularly on cladding pressures. Wind loads on com- 
plicated shapes are frequently smaller than those on the 
simpler shapes of Figures 6-3 through 6-8, and so wind 
loads determined from these provisions reasonably enve- 
lope most structure shapes. Buildings which are clearly 
unusual should use the provisions of Section 6.4 for wind- 
tunnel tests. 

RIGID BUILDINGS AND OTHER STRUCTURES. 
The defining criterion for rigid, in comparison to flex- 
ible, is that the natural frequency is greater than or 
equal to 1 Hz. A general guidance is that most rigid 
buildings and structures have height-to-minimum-width 
ratio of less than 4. Where there is concern about 
whether or not a building or structure meets this require- 
ment, the provisions of Section 9 provide a method 
for calculating natural frequency (period = 1/natural fre- 
quency). 

WIND-BORNE DEBRIS REGIONS. Some buildings 
located in a wind-borne debris region may not be vul- 
nerable to wind-borne debris. For example, an isolated 
building located a substantial distance from natural and 
man-made debris sources would unlikely be impacted by 



debris, provided that building components from the building 
itself were not blown off, and provided that refuse contain- 
ers, lawn furniture, and other similar items where not in 
the vicinity of the building. However, ASCE 7 does not 
allow an exception for such buildings to be excluded from 
the requirements applicable to buildings in a wind-borne 
debris region. 

Although wind-borne debris can occur in just about any 
condition, the level of risk in comparison to the postu- 
lated debris regions and impact criteria may also be lower 
than that determined for the purpose of standardization. 
This possibility also applies to the "transition zone" as 
described above. For example, individual buildings may 
be sited away from likely debris sources that would gen- 
erate significant risk of impacts similar in magnitude to 
pea gravel (i.e., as simulated by 2 g steel balls in impact 
tests) or butt-on 2x4 impacts as required in impact test- 
ing criteria. This situation describes a condition of low 
vulnerability only as a result of limited debris sources 
within the vicinity of the building. In other cases, poten- 
tial sources of debris may be present, but extenuating 
conditions can lower the risk. These extenuating condi- 
tions include the type of materials and surrounding con- 
struction, the level of protection offered by surrounding 
exposure conditions, and the design wind speed. There- 
fore, the risk of impact may differ from those postulated 
as a result of the conditions specifically enumerated in the 
standard and the referenced impact standards. The com- 
mittee recognizes that there are vastly differing opinions, 
even within the Standards Committee, regarding the signif- 
icance of these parameters that are not fully considered 
in developing standardized debris regions or referenced 
impact criteria. 



SECTION C6.3 
SYMBOLS AND NOTATION 

The following additional symbols and notation are used 
herein: 

A £j = average area of open ground surrounding each 

obstruction; 
n = reference period, in years; 
P a = annual probability of wind speed exceeding a 

given magnitude (see Eq. C6-1); 
P n ~ probability of exceeding design wind speed 

during n years (see Eq. C6-1); 
s b — average frontal area presented to the wind by 

each obstruction; 
V r = wind speed averaged over t seconds (see 

Figure C6-2), in mph (m/s); 
V3600 — mean wind speed averaged over 1 hour (see 

Figure C6-2), in mph (m/s); 
p = structural damping coefficient (percentage of 

critical damping). 



272 



ASCE 7-02 



SECTION G6.4 
METHOD 1 - SIMPLIFIED PROCEDURE 

Method 1 has been added to the Standard for a designer 
having the relatively common low-rise (h < 60 ft) regu- 
lar shaped, simple diaphragm building case (see defini- 
tions for "simple diaphragm building" and "regular shaped 
building") where pressures for the roof and walls can be 
selected directly from a table. Two figures are provided: 
Figure 6-2 for the main wind force-resisting system and 
Figure 6-3 for components and cladding. Values are pro- 
vided for enclosed buildings. Note that for the main wind 
force-resisting system in a diaphragm building, the inter- 
nal pressure cancels for loads on the walls, but must be 
considered for the roof. This is true because when wind 
forces are transferred by horizontal diaphragms (such as 
floors and roofs) to the vertical elements of the main wind 
force-resisting system (such as shear walls, X-bracing, or 
moment frames), the collection of wind forces from wind- 
ward and leeward sides of the building occurs in the hor- 
izontal diaphragms. Once transferred into the horizontal 
diaphragms by the wall systems, the wind forces become 
a net horizontal wind force that is delivered to the vertical 
elements. The equal and opposite internal pressures on the 
walls cancel in the horizontal diaphragm. Method 1 com- 
bines the windward and leeward pressures into a net hori- 
zontal wind pressure, with the internal pressures canceled. 
The user is cautioned to consider the precise application of 
windward and leeward wall loads to members of the roof 
diaphragm where openings may exist and where particu- 
lar members such as drag struts are designed. The design 
of the roof members of the main wind force-resisting sys- 
tem is still influenced by internal pressures, but for simple 
diaphragm buildings with roof angles below 25 degrees, 
it can be assumed that the maximum uplift, produced by 
a positive internal pressure, is the controlling load case. 
From 25 to 45 degrees, both positive and negative inter- 
nal pressure cases (Load Cases 1 and 2, respectively) must 
be checked for the roof, since the windward roof external 
pressure becomes positive at that point. 

For the designer to use Method 1 for the design of 
the MWFRS, the building must conform to all eight 
requirements in 6.4.1.1; otherwise Method 2 or 3 must be 
used. Values are tabulated for Exposure B at h — 30 ft, 
and / = 1.0. Multiplying factors are provided for other 
exposures and heights. The following values have been used 
in preparation of the tables: 

h = 30 ft Exposure B K z = 0.70 
K d - 0.85 K zt = 1.0 / = 1.0 
GC pi = ±0.18 (enclosed building) 

Pressure coefficients are from Figures 6-10 and 6-11. 

Wall elements resisting two or more simultaneous wind- 
induced structural actions (such as bending, uplift, or 
shear) should be designed for the interaction of the wind 
loads as part of the main wind force- resisting system. 



The horizontal loads in Figure 6-2 are the sum of the 
windward and leeward pressures, and are therefore not 
applicable as individual wall pressures for the interaction 
load cases. Design wind pressures, p s for Zones A and 
C should be multiplied by +0.85 for use on windward 
walls and by —0.70 for use on leeward walls (plus sign 
signifies pressures acting toward the wall surface). For 
side walls, p s for zone C multiplied by -0.65 should be 
used. These wall elements must also be checked for the 
various separately acting (not simultaneous) component and 
cladding load cases. 

Main wind force-resisting roof members spanning at 
least from the eave to the ridge or supporting members 
spanning at least from eave to ridge are not required to be 
designed for the higher end zone loads. The interior zone 
loads should be applied. This is due to the enveloped nature 
of the loads for roof members. 

The component and cladding tables in Figure 6-3 are 
not related to the simple diaphragm methodology, but are 
a tabulation of the pressures on an enclosed, regular, 30- 
ft-high building with a roof as described. The pressures 
can be modified to a different exposure and height with 
the same adjustment factors as the MWFRS pressures. 
For the designer to use Method 1 for the design of the 
components and cladding, the building must conform to all 
five requirements in 6.4.1.2 otherwise Method 2 or 3 must 
be used. A building may qualify for use of Method 1 for its 
components and cladding only, in which case, its MWFRS 
should be designed using Method 2 or 3. 



SECTION C6.5 

METHOD 2 - ANALYTICAL PROCEDURE 

C6.5.1 Scope. The analytical procedure provides wind 
pressures and forces for the design of main wind force- 
resisting systems and for the design of components and 
cladding of buildings and other structures. The proce- 
dure involves the determination of wind directionality and 
a velocity pressure, the selection or determination of an 
appropriate gust effect factor, and the selection of appro- 
priate pressure or force coefficients. The procedure allows 
for the level of structural reliability required, the effects of 
differing wind exposures, the speed-up effects of certain 
topographic features such as hills and escarpments, and 
the size and geometry of the building or other structure 
under consideration. The procedure differentiates between 
rigid and flexible buildings and other structures, and the 
results generally envelope the most critical load conditions 
for the design of main wind force-resisting systems as well 
as components and cladding. 

The Standard in Section 6.5.4 requires that a structure be 
designed for winds from all directions. A rational procedure 
to determine directional wind loads is as follows. Wind 
load for buildings using Section 6.5.12.2.1 and Figure 6-6 
or Figure 6-7 are determined for eight wind directions 



Minimum Design Loads for Buildings and Other Structures 



273 



at 45 -degree intervals, with four falling along primary 
building axes as shown in Figure C6-1. For each of the 
eight directions, upwind exposure is determined for each 
of two 45-degree sectors, one on each side of the wind 
direction axis. The sector with the exposure giving highest 
loads will be used to define wind loads for that direction. 
For example, for winds from the north, the exposure from 
sector one or eight whichever gives the highest load is used; 
for wind from the east, the exposure from sector two or 
three whichever gives the highest load is used; for wind 
coming from the northeast, the most exposed of sectors one 
or two is used to determine full x and y loading individually, 
and then 75% of these loads are to be applied in each 
direction at the same time according to the requirements 
of Section 6.5.123 and Figure 6-9. See Section C6.5.6 for 
further discussion of exposures. The procedure defined in 
this Section for determining wind loads in each design 
direction is not to be confused with the determination of 
the wind directionality factor k c i in Eq. 6-15. The kd factor 
determined from Section 6.5.4 and Table 6-4 applies for all 
design wind directions (see Section C6.5.4.4). 

Wind loads for cladding elements are determined using 
the upwind exposure for the single surface roughness in one 
of the eight sectors of Figure C6-1 which gives the highest 
cladding pressures. 

C6.5.2 Limitations of Analytical Procedure. The provi- 
sions given under Section 6.5.2 apply to the majority of site 
locations and buildings and structures, but for some loca- 
tions, these provisions may be inadequate. Examples of site 
locations and buildings and structures (or portions thereof) 
that require use of recognized literature for documentation 
pertaining to wind effects, or the use of the wind-tunnel 
procedure of Section 6.6 include: 

1. Site locations that have channeling effects or wakes 
from upwind obstructions. Channeling effects can 
be caused by topographic features (e.g., mountain 
gorge) or buildings (e.g., a cluster of tall buildings). 
Wakes can be caused by hills or by buildings or 
other structures. 

2. Buildings with unusual or irregular geometric shape, 
including barrel vaults, and other buildings whose 
shape (in plan or profile) differs significantly from 
a uniform or series of superimposed prisms simi- 
lar to those indicated in Figures 6-3 through 6-8. 
Unusual or irregular geometric shapes include build- 
ings with multiple setbacks, curved facades, irregular 
plan resulting from significant indentations or projec- 
tions, openings through the building, or multitower 
buildings connected by bridges. 

3. Buildings with unusual response characteristics, which 
result in across-wind and/or dynamic torsional loads, 
loads caused by vortex shedding, or loads result- 
ing from instabilities such as flutter or galloping. 



Examples of buildings and structures which may have 
unusual response characteristics include flexible build- 
ings with natural frequencies normally below 1 Hz, 
tall slender buildings (building height-to-width ratio 
exceeds 4), and cylindrical buildings or structures. 
Note: Vortex shedding occurs when wind blows across 
a slender prismatic or cylindrical body. Vortices are 
alternately shed from one side of the body and then 
the other side, which results in a fluctuating force act- 
ing at right angles to the wind direction (across-wind) 
along the length of the body. 

4. Bridges, cranes, electrical transmission lines, guyed 
masts, telecommunication towers, and flagpoles. 

C6.5.2.1 Shielding. Due to the lack of reliable analytical 
procedures for predicting the effects of shielding provided 
by buildings and other structures or by topographic features, 
reductions in velocity pressure due to shielding are not 
permitted under the provisions of Section 6.5. However, 
this does not preclude the determination of shielding effects 
and the corresponding reductions in velocity pressure by 
means of the wind-tunnel procedure in Section 6.6. 

C6.5.2.2 Air-Perraeable Cladding. Air-permeable roof or 
wall claddings allow partial air pressure equalization 
between their exterior and interior surfaces. Examples 
include siding, pressure-equalized rain screen walls, 
shingles, tiles, concrete roof pavers, and aggregate 
roof surfacing. 

The design wind pressures derived from Section 6.5 rep- 
resent the pressure differential between the exterior and 
interior surfaces of the exterior envelope (wall or roof sys- 
tem). Because of partial air-pressure equalization provided 
by air-permeable claddings, the pressures derived from 
Section 6.5 can overestimate the load on air-permeable 
cladding elements. The designer may elect either to use the 
loads derived from Section 6.5 or to use loads derived by 
an approved alternative method. If the designer desires to 
determine the pressure differential across the air-permeable 
cladding element, appropriate full-scale pressure measure- 
ments should be made on the applicable cladding element, 
or reference be made to recognized literature [C6-9, C6-16, 
C6-37, C6-73] for documentation pertaining to wind loads. 

C6.5.4 Basic Wind Speed. The ASCE 7 wind map in- 
cluded in the 1998 Standard and again for the 2002 edition 
has been updated from the map in ASCE 7-95 based 
on a new and more complete analysis of hurricane wind 
speeds [C6-78, C6-79]. This new hurricane analysis yields 
predictions of 50- and 100-year return period peak gust 
wind speeds along the coast, which are generally similar to 
those given in References [C6-88 and C6-89]. The decision 
within the Task Committee on Wind Loads to update the 
map relied on several factors important to an accurate wind 
specification: 



274 



ASCE 7-02 



1. The new hurricane results include many more pre- 
dictions for sites away from the coast than have been 
available in the past. It is desirable to include the 
best available decrease in speeds with inland distance. 
Significant reductions in wind speeds occur in inland 
Florida for the new analysis. 

2. The distance inland to which hurricanes can influence 
wind speed increases with return period. It is desirable 
to include this distance in the map for design of 
ultimate events (working stress multiplied by an 
appropriate load factor). 

3. A hurricane coast importance factor of 1 .05 acting on 
wind speed was included explicitly in past ASCE 7 
Standards (1993 and earlier) to account for the more 
rapid increase of hurricane speeds with return period 
in comparison to non-hurricane winds. The hurricane 
coast importance factor actually varies in magnitude 
and position along the coast and with distance inland. 
In order to produce a more uniform risk of failure, 
it is desirable to include the effect of the importance 
factor in the map by first mapping an ultimate event 
and then reducing the event to a design basis. 

The Task Committee on Wind Loads chose to use a 
map which includes the hurricane importance factor in 
the map contours. The map is specified so that the loads 
calculated from the Standard, after multiplication by the 
load factor, represent an ultimate load having approximately 
the same return period as loads for non-hurricane winds. 
(An alternative not selected was to use an ultimate wind 
speed map directly in the standard, with a load factor 
of 1.0). 

The approach required selection of an ultimate return 
period. A return period of about 500 years has been used 
previously for earthquake loads. This return period can be 
derived from the non-hurricane speeds in ASCE 7-95. A 
factor of 0.85 is included in the load factor of ASCE 7-95 to 
account for wind and pressure coefficient directionality [C6- 
76]. Removing this from the load factor gives an effective 
load factor F of 1.30/0.85 - 1.529 (round to 1.5). Of the 
uncertainties affecting the wind load factor, the variability 
in wind speed has the strongest influence [C6-77], such that 
changes in the coefficient of variation in all other factors 
by 25% gives less than a 5% change in load factor. The 
non-hurricane multiplier of 50-year wind speed for various 
return periods averages Fc — 0.36 + 0.1 In (127), with 
T in years [C6-74]. Setting Fc = JF = ^1.5 = 1.225 
yields T = 476 years. On this basis, a 500-year speed 
can reasonably represent an approximate ultimate limit 
state event. 

A set of design level hurricane speed contours, which 
include the hurricane importance factor, were obtained 
by dividing 500-year hurricane wind speed contours by 
*JF = 1.225. The implied importance factor ranges from 
near 1 .0 up to about 1 .25 (the explicit value in ASCE 7-93 
is 1.05). 



The design level speed map has several advantages. 
First, a design using the map results in an ultimate load 
(loads inducing the design strength after use of the load 
factor) which has a more uniform risk for buildings than 
occurred with earlier versions of the map. Second, there is 
no need for a designer to use and interpolate a hurricane 
coast importance factor. It is not likely that the 500-year 
event is the actual speed at which engineered structures 
are expected to fail, due to resistance factors in materials, 
due to conservative design procedures which do not always 
analyze all load capacity, and due to a lack of a precise 
definition of "failure." 

The wind speed map of Figure 6-1 presents basic 
wind speeds for the contiguous United States, Alaska, 
and other selected locations. The wind speeds correspond 
to 3-second gust speeds at 33 ft (10 m) above ground 
for Exposure Category C. Because the National Weather 
Service has phased out the measurement of fastest-mile 
wind speeds, the basic wind speed has been redefined as 
the peak gust which is recorded and archived for most 
NWS stations. Given the response characteristics of the 
instrumentation used, the peak gust is associated with an 
averaging time of approximately 3 seconds. Because the 
wind speeds of Figure 6-1 reflect conditions at airports 
and similar open-country exposures, they do not account 
for the effects of significant topographic features such as 
those described in Section 6.5.7. Note that the wind speeds 
shown in Figure 6-1 are not representative of speeds at 
which ultimate limit states are expected to occur. Allowable 
stresses or load factors used in the design equation(s) lead 
to structural resistances and corresponding wind loads and 
speeds that are substantially higher than the speeds shown 
in Figure 6-1. 

The hurricane wind speeds given in Figure 6-1 replace 
those given in ASCE-7-95, which were based on a com- 
bination of the data given in References [C6-5, C6-15, 
C6-54, C6-88, and C6-20], supplemented with some judg- 
ment. The non- hurricane wind speeds of Figure 6-1 were 
prepared from peak gust data collected at 485 weather sta- 
tions where at least 5 years of data were available [C6-29, 
C6-30, C6-74]. For non-hurricane regions, measured gust 
data were assembled from a number of stations in state- 
sized areas to decrease sampling error, and the assembled 
data were fit using a Fisher-Tippett Type I extreme value 
distribution. This procedure gives the same speed as does 
area- averaging the 50-year speeds from the set of stations. 
There was insufficient variation in 50- year speeds over the 
eastern 3/4 of the lower 48 states to justify contours. The 
division between the 90 and 85 mph (40.2 and 38.0 m/s) 
regions, which follows state lines, was sufficiently close to 
the 85 mph (38.0 m/s) contour that there was no statisti- 
cal basis for placing the division off political boundaries. 
This data is expected to follow the gust factor curve of 
Figure C6-2 [C6-13], 

Limited data were available on the Washington and 
Oregon coast; in this region, existing fastest-mile wind 



Minimum Design Loads for Buildings and Other Structures 



275 



speed data were converted to peak gust speeds using open- 
country gust factors [C6-13]. This limited data indicates 
that a speed of 100 mph is appropriate in some portions 
of the special coastal region in Washington and 90 mph 
in the special coastal region in Oregon; these speeds do 
not include that portion of the special wind region in 
the Columbia River Gorge, where higher speeds may be 
justified. Speeds in the Aleutian Islands and in the interior 
of Alaska were established from gust data. Contours in 
Alaska are modified slightly from ASCE 7-88 based on 
measured data, but insufficient data were available for a 
detailed coverage of the mountainous regions. 

C6.5.4.1 Special Wind Regions. Although the wind- 
speed map of Figure 6-1 is valid for most regions of the 
country, there are special regions in which wind-speed 
anomalies are known to exist. Some of these special regions 
are noted in Figure 6-1. Winds blowing over mountain 
ranges or through gorges or river valleys in these special 
regions can develop speeds that are substantially higher than 
the values indicated on the map. When selecting basic wind 
speeds in these special regions, use of regional climatic 
data and consultation with a wind engineer or meteorologist 
is advised. 

It is also possible that anomalies in wind speeds exist 
on a micrometeorological scale. For example, wind speed- 
up over hills and escarpments is addressed in Section 6.5.7. 
Wind speeds over complex terrain may be better determined 
by wind-tunnel studies as described in Section 6.6. Adjust- 
ments of wind speeds should be made at the micrometeoro- 
logical scale on the basis of wind engineering or meteoro- 
logical advice and used in accordance with the provisions 
of Section 6.5.4.2 when such adjustments are warranted. 

C6.5.4.2 Estimation of Basic Wind Speeds from 
Regional Climatic Data. When using regional climatic 
data in accordance with the provisions of Section 6.5.4.2 
and in lieu of the basic wind speeds given in Figure 6-1, 
the user is cautioned that the gust factors, velocity 
pressure exposure coefficients, gust effect factors, pressure 
coefficients, and force coefficients of this Standard are 
intended for use with the 3 -second gust speed at 33 ft 
(10 m) above ground in open country. It is necessary, 
therefore, that regional climatic data based on a different 
averaging time, for example, hourly mean or fastest mile, 
be adjusted to reflect peak gust speeds at 33 ft (10 m) 
above ground in open country. The results of statistical 
studies of wind-speed records, reported by [C6-13] for 
extratropical winds and for hurricanes [C6-78], are given 
in Figure C6-2, which defines the relation between wind 
speed averaged over t seconds, V t , and over one hour, V3600. 
New research cited in [C6-78] indicates that the old Krayer- 
Marshall curve [C6-20] does not apply in hurricanes. 
Therefore it was removed in Figure C6-1 in ASCE 7-98. 
The gust factor adjustment to reflect peak gust speeds is not 



always straightforward, and advice from a wind engineer or 
meteorologist may be needed. 

In using local data, it should be emphasized that sam- 
pling errors can lead to large uncertainties in specification 
of the 50-year wind speed. Sampling errors are the errors 
associated with the limited size of the climatological data 
samples (years of record of annual extremes). It is possible 
to have a 20 mph (8.9 m/s) error in wind speed at an indi- 
vidual station with a record length of 30 years. It was this 
type of error that led to the large variations in speed in the 
non-hurricane areas of the ASCE 7-88 wind map. While 
local records of limited extent often must be used to define 
wind speeds in special wind areas, care and conservatism 
should be exercised in their use. 

If meteorological data are used to justify a wind speed 
lower than 85 mph 50-year peak gust at 10 m, an analysis 
of sampling error is required to demonstrate that the wind 
record could not occur by chance. This can be accomplished 
by showing that the difference between predicted speed and 
85 mph contains 2 to 3 standard deviations of sampling 
error [C6-67]. Other equivalent methods may be used. 

C6.5.4.3 Limitation. In recent years, advances have been 
made in understanding the effects of tornadoes on buildings. 
This understanding has been gained through extensive doc- 
umentation of building damage caused by tornadic storms 
and through analysis of collected data. It is recognized that 
tornadic wind speeds have a significantly lower probabil- 
ity of occurrence at a point than the probability for basic 
wind speeds. In addition, it is found that in approximately 
one-half of the recorded tornadoes, gust speeds are less 
than the gust speeds associated with basic wind speeds. In 
intense tornadoes, gust speeds near the ground are in the 
range of 150 to 200 mph (67-89 m/s). Sufficient informa- 
tion is available to implement tornado-resistant design for 
above-ground shelters and for buildings that house essential 
facilities for post-disaster recovery. This information is in 
the form of tornado risk probabilities, tornadic wind speeds, 
and associated forces. Several references provide guidance 
in developing wind load criteria for tornado-resistant design 
[C6-1, C6-2, C6-24-C6-28, C6-57]. 

Tornadic wind speeds, which are gust speeds, associated 
with an annual probability of occurrence of 1 x 10~ 5 
(100,000 year mean recurrence interval) are shown in 
Figure C6-3. This map was developed by the American 
Nuclear Society committee ANS 2.3 in the early 1980s. 
Tornado occurrence data of the last 15 years can provide a 
more accurate tornado hazard wind speed for a specific site. 

C6.5.4.4 Wind Directionality Factor. The existing wind 
load factor 1.3 in ASCE 7-95 includes a "wind direction- 
ality factor" of 0.85 [C6-76, C6-77]. This factor accounts 
for two effects: (1) The reduced probability of maximum 
winds coming from any given direction and (2) the reduced 
probability of the maximum pressure coefficient occurring 



276 



ASCE 7-02 



for any given wind direction. The wind directionality factor 
(identified as Kd in the Standard) has been hidden in pre- 
vious editions of the Standard and has generated renewed 
interest in establishing the design values for wind forces 
determined by using the Standard. Accordingly, the Task 
Committee on Wind Loads, working with the Task Com- 
mittee on Load Combinations, has decided to separate the 
wind directionality factor from the load factor and include 
its effect in the equation for velocity pressure. This has 
been done by developing a new factor, K d , that is tab- 
ulated in Table 6-4 for different structure types. As new 
research becomes available, this factor can be directly mod- 
ified without changing the wind load factor. Values for the 
factor were established from references in the literature and 
collective committee judgment. It is noted that the k c \ value 
for round chimneys, tanks, and similar structures is given as 
0.95 in recognition of the fact that the wind load resistance 
may not be exactly the same in all directions as implied by 
a value of 1.0. A value of 0.85 might be more appropriate 
if a triangular trussed frame is shrouded in a round cover. 
1.0 might be more appropriate for a round chimney having 
a lateral load resistance equal in all directions. The designer 
is cautioned by the footnote to Table 6-4 and the statement 
in Section 6.5.4.4, where reference is made to the fact that 
this factor is only to be used in conjunction with the load 
combination factors specified in 2.3 and 2.4. 



For applications of serviceability, design using maxi- 
mum likely events, or other applications, it may be desired 
to use wind speeds associated with mean recurrence inter- 
vals other than 50 years. To accomplish this, the 50-year 
speeds of Figure 6-1 are multiplied by the factors listed 
in Table C6-2. Table C6-2 is strictly valid for the non- 
hurricane winds only (V < 100 mph for continental United 
States and all speeds in Alaska), where the design wind 
speeds have a nominal annual exceedance probability of 
0.02. Using the factors given in Table C6-2 to adjust the 
hurricane wind speeds will yield wind speeds and result- 
ing wind loads that are approximately risk consistent with 
those derived for the non- hurricane-prone regions. The 
true return periods associated with the hurricane wind 
speeds cannot be determined using the information given 
in this Standard. 

The difference in wind speed ratios between continental 
United States (V < 100 mph) and Alaska were determined 
by data analysis and probably represent a difference in 
climatology at different latitudes. 

C6.5.6 Exposure Categories. A number of revisions have 
been made to the definitions of exposure categories in 
the ASCE 7-02 edition. In ASCE 7-98 the definitions of 
Exposures C and D were modified based on new research 
[C6-86]. Further changes in the new edition are: 



C6.5.5 Importance Factor. The importance factor is used 
to adjust the level of structural reliability of a building 
or other structure to be consistent with the building clas- 
sifications indicated in Table 1-1. The importance factors 
given in Table 6-1 adjust the velocity pressure to different 
annual probabilities of being exceeded. Importance-factor 
values of 0.87 and 1.15 are, for the non-hurricane winds, 
associated, respectively, with annual probabilities of being 
exceeded by 0.04 and 0.01 (mean recurrence intervals of 25 
and 100 years). In the case of hurricane winds, the annual 
exceedance probabilities implied by the use of the impor- 
tance factors of 0.77 and 1.15 will vary along the coast; 
however, the resulting risk levels associated with the use 
of these importance factors when applied to hurricane winds 
will be approximately consistent with those applied to the 
non-hurricane winds. 

The probability P n that the wind speed associated with a 
certain annual probability P a will be equaled or exceeded at 
least once during an exposure period of n years is given by 



P n = 1 - (1 - PaT 



(Eq. C6-1) 



and values of P n for various values of P a and n are listed in 
Table C6-1. As an example, if a design wind speed is based 
upon P a = 0.02 (50-year mean recurrence interval), there 
exists a probability of 0.40 that this speed will be equaled 
or exceeded during a 25-year period, and a 0.64 probability 
of being equaled or exceeded in a 50-year period. 



1. Exposure A has been deleted. In the past, Exposure A 
was intended for heavily built-up city centers with 
tall buildings. However, the committee has concluded 
that in areas in close proximity to tall buildings 
the variability of the wind is too great, because of 
local channeling and wake buffeting effects, to allow 
a special category A to be defined. For projects 
where schedule and cost permit, in heavily built- 
up city centers, Method 3 is recommended since 
this will enable local channeling and wake buffeting 
effects to be properly accounted for. For all other 
projects, Exposure B can be used, subject to the 
limitations in 6.5.2. 

2. A distinction has been made between surface rough- 
ness categories and exposure categories. This has 
enabled more precise definitions of Exposures B, C, 
and D to be obtained in terms of the extent and types 
of surface roughness that are upwind of the site. The 
requirements for the upwind fetch have been modified 
based on recent investigations into effects of rough- 
ness changes and transitions between them [C6-90]. 

3. The exposure for each wind direction is now defined 
as the worst case of the two 45-degree sectors either 
side of the wind direction being considered (see also 
Section C6.5.4). 

4. Interpolation between exposure categories is now 
permitted. One acceptable method of interpolating 
between exposure categories is provided in C6.5.6.4. 



Minimum Design Loads for Buildings and Other Structures 



277 



The descriptions of the surface roughness categories and 
exposure categories in Section 6.5.6 have been expressed as 
far as is possible in easily understood verbal terms which 
are sufficiently precise for most practical applications. For 
cases where the designer wishes to make a more detailed 
assessment of the surface roughness category and exposure 
category, the following more mathematical description is 
offered for guidance. The ground surface roughness is best 
measured in terms of a roughness length parameter called 
Zo- Each of the surface roughness categories B through D 
corresponds to a range of values of this parameter, as does 
the even rougher category A used in earlier versions of 
the Standard in heavily built-up urban areas but removed 
in the present edition. The range of zo in meters (ft) for 
each terrain category is given in the boxed text below. 
Exposure A has been included in the table below as a 
reference which may be useful when using Method 3 (the 
wind tunnel procedure). 











so Inherent in 




Lowe J' 


Typical 


Upper 


Tabulated K, 


Exposure 


Limit of 


Value of 


Limit of 


Values in Sec. 


Category 


zo, m. (ft) 


zo, m (ft) 


zo, m (ft) 


6.5.6.4. m (ft) 


A 


0.7 (2.3) < zo 


2 (6.6) 


— 


— 


B 


0.1.5 (0.49) <zo 


0.3 (0.98) 


so < 0.7 (2.3) 


0.15 (0.49) 


C 


0.01 (0.033) < zo 


0.02 (0.066) 


zo < 0.15 (0.49) 


0.02 (0.066) 


D 


— 


0.005 (0.0.16) 


zo < 0.01 (0.033) 


0.005 (0.016) 



The value of zo for a particular terrain can be estimated 
from the typical dimensions of surface roughness elements 
and their spacing on the ground area using an empirical 
relationship, due to Lettau [C6-75], which is 



<.o 



0.5//, 



of 



Job 



iob 



(Eq. C6-2) 



where 



H ob — the average height of the roughness in the 

upwind terrain, 
S oh = the average vertical frontal area per obstruction 

presented to the wind, 
A Ob — the average area of ground occupied by each 

obstruction, including the open area surrounding it. 

Vertical frontal area is defined as the area of the 
projection of the obstruction onto a vertical plane normal 
to the wind direction. The area S b may be estimated 
by summing the approximate vertical frontal areas of all 
obstructions within a selected area of upwind fetch and 
dividing the sum by the number of obstructions in the area. 
The average height H may be estimated in a similar way 
by averaging the individual heights rather than using the 
frontal areas. Likewise A ob may be estimated by dividing 
the size of the selected area of upwind fetch by the number 
of obstructions in it. 

As an example, if the upwind fetch consists primarily 
of single-family homes with typical height H — 6 m, 
vertical frontal area 60 sq m, and ground area per home 



of 1200 sq m, then zq is calculated to be zo = 0.5 x 6 x 
60/1200 = 0.15 m, which falls into exposure category B 
according to the above table. Note that often a suburban 
area will have many trees which would add to the effective 
vertical frontal area per home, significantly increasing the 
ratio S ob /A ob . 

Trees and bushes are porous and are deformed by strong 
winds, which reduces their effective frontal areas [C6-91]. 
For conifers and other evergreens no more than 50% of their 
gross frontal area can be taken to be effective in obstructing 
the wind. For deciduous trees and bushes no more than 15% 
of their gross frontal area can be taken to be effective in 
obstructing the wind. Gross frontal area is defined in this 
context as the projection onto a vertical plane (normal to 
the wind) of the area enclosed by the envelope of the tree 
or bush. 

A recent study [C6-66] has estimated that the majority of 
buildings (perhaps as much as 60%-80%) have an exposure 
category corresponding to Exposure B. While the relatively 
simple definition in the Standard will normally suffice for 
most practical applications, oftentimes the designer is in 
need of additional information, particularly with regard to 
the effect of large openings or clearings (such as large 
parking lots, freeways, or tree clearings) in the otherwise 
"normal" ground surface roughness B. The following is 
offered as guidance for these situations: 

1. The simple definition of Exposure B given in the 
body of the Standard, using the new surface rough- 
ness category definition, is shown pictorially in 
Figure C6-4. This definition applies for the surface 
roughness B condition prevailing 2630 ft (800 m) 
upward with insufficient "open patches" as defined 
below to disqualify the use of Exposure B. 

2. An opening in the surface roughness B large enough 
to have a significant effect on the exposure category 
determination is defined as an "open patch." An open 
patch is defined as an opening greater than or equal 
to 164 ft (50 m) on each side (i.e., greater than 165 ft 
(50 m) by 164 ft (50 m)). Openings smaller than 
this need not be considered in the exposure category 
determination. 

3. The effect of open patches of surface roughness C 
or D on the use of Exposure Category B is shown 
pictorially in Figures C6-5 and C6-6. Note that the 
plan location of any open patch may have a different 
effect for different wind directions. 

Aerial photographs, representative of each exposure 
type, are included in the commentary to aid the user in 
establishing the proper exposure for a given site. Obviously, 
the proper assessment of exposure is a matter of good 
engineering judgment. This fact is particularly true in light 
of the possibility that the exposure could change in one 
or more wind directions due to future demolition and/or 
development. 



278 



ASCE 7-02 






EXPOSURE B 

SUBURBAN RESIDENTIAL AREA WITH MOSTLY SINGLE-FAMILY DWELLINGS. STRUCTURES IN THE CENTER OF THE 

PHOTOGRAPH HAVE SITES DESIGNATED AS EXPOSURE B WITH SURFACE ROUGHNESS CATEGORY B TERRAIN AROUND THE 

SITE FOR A DISTANCE GREATER THAN 1500 FT OR TEN TIMES THE HEIGHT OF THE STRUCTURE, WHICHEVER IS GREATER, IN 

ANY WIND DIRECTION 













EXPOSURE B 

URBAN AREA WITH NUMEROUS CLOSELY SPACED OBSTRUCTIONS HAVING THE SIZE OF SINGLE-FAMILY DWELLINGS OR 

LARGER. FOR ALL STRUCTURES SHOWN, TERRAIN REPRESENTATIVE OF SURFACE ROUGHNESS CATEGORY B EXTENDS MORE 

THAN TEN TIMES THE HEIGHT OF THE STRUCTURE OR 800 M, WHICHEVER IS GREATER, IN THE UPWIND DIRECTION 



Minimum Design Loads for Buildings and Other Structures 



279 




EXPOSURE B 
STRUCTURES IN THE FOREGROUND ARE LOCATED IN EXPOSURE B. STRUCTURES IN THE CENTER TOP OF THE PHOTOGRAPH 
ADJACENT TO THE CLEARING TO THE LEFT, WHICH IS GREATER THAN 200 M SN LENGTH, ARE LOCATED IN EXPOSURE C WHEN 

WIND COMES FROM THE LEFT OVER THE CLEARING (SEE FIGURE C6-5) 









'. , ■■■■■ :. . V ■■ ■■.■■::■■: 



;..::.. J;;:, ■ . r V 






/;4l* v > 



. .V-'--'- •• \,, I 



*%s#* 



^-^■^■■.^..yy-; yty~»'-- j^y.y.-^y y y;-&;: 











EXPOSURE C 
FLAT OPEN GRASSLAND WITH SCATTERED OBSTRUCTIONS HAVING HEIGHTS GENERALLY LESS THAN 30 FT 



280 



ASCE 7-02 










EXPOSURE C 

OPEN TERRAIN WITH SCATTERED OBSTRUCTIONS HAVING HEIGHTS GENERALLY LESS THAN 30 FT FOR MOST WIND 

DIRECTIONS, ALL 1 -STORY STRUCTURES WITH A MEAN ROOF HEIGHT LESS THAN 30 FT IN THE PHOTOGRAPH ARE LESS THAN 

1500 FT OR TEN TIMES THE HEIGHT OF THE STRUCTURE, WHICHEVER IS GREATER, FROM AN OPEN FIELD THAT PREVENTS THE 

USE OF EXPOSURE B 






auk 

MRS 






G-J 






mm, : sSaJJiiB?: 












EXPOSURE D 

A BUILDING AT THE SHORELINE (EXCLUDING SHORELINES IN HURRICANE-PRONE REGIONS) WITH WIND FLOWING OVER OPEN 

WATER FOR A DISTANCE OF AT LEAST 1 MILE. SHORELINES IN EXPOSURE D INCLUDE INLAND WATERWAYS, THE GREAT LAKES, 

AND COASTAL AREAS OF CALIFORNIA, OREGON, WASHINGTON, AND ALASKA 



Minimum Design Loads for Buildings and Other Structures 



281 



C6.5.6.4 Velocity Pressure Exposure Coefficient. The 
velocity pressure exposure coefficient K z can be obtained 
using the equation: 



K, = 



2.01 



2.01 



15 



2/a 



2/a 



for 15 ft < z < z z 



for z < 15 ft 



(Eq. C6-3a) 



(Eq. C6-3b) 

in which values of a and z 8 are given in Table 6-2. These 
equations are now given in Table 6-3 to aid the user. 

In ASCE 7-95, the values of a and the preceding 
formulae were adjusted to be consistent with the 3-second 
gust format introduced at that time. Other changes were 
implemented in ASCE 7-98 including truncation of K z 
values for Exposure A and B below heights of 100 ft and 
30 ft, respectively. Exposure A has been eliminated in the 
2002 edition. 

In the ASCE 7-02 standard, the K z expressions are 
unchanged from ASCE 7-98. However, the possibility of 
interpolating between the standard exposures is recog- 
nized in the present edition. One rational method is pro- 
vided below. 

To a reasonable approximation, the empirical exponent 
a and gradient height z g in Eqs. C6-3a and C6-3b for 
exposure coefficient K z may be related to the roughness 
length z,{) by the relations 



c t*o 



-0.157 



and 



where 



7 0.125 

Zg - C2Z 



(Eq, C6-5) 



Units ofZfyZg 


C\ 


C2 


m 


5.14 


450 


ft 


6.19 


1273 



The above relationships are based on matching the 
ESDU boundary layer model [C6-90 to C6-92] empirically 
with the power law relationship in Eq. C6-3a, b, the ESDU 
model being applied at latitude 45 degrees with a gradient 
wind of 50 m/s. If z.q has been determined for a particular 
upwind fetch, Eq. C6-3, C6-4, and C6-5 can be used 
to evaluate K z . The correspondence between zo and the 
parameters a and z g implied by these relationships does 
not align exactly with that described in the commentary 
to ASCE 7-95 and 7-98. However, the differences are 
relatively small and not of practical consequence. The 
ESDU boundary layer model has also been used to derive 
the following simplified method of evaluating K 7 following 
a transition from one surface roughness to another. For 
more precise estimates the reader is referred to the original 
ESDU model [C6-90 to C6-92]. 



In uniform terrain, the wind travels a sufficient distance 
over the terrain for the planetary boundary layer to reach 
an equilibrium state. The exposure coefficient values in 
Table 6-3 are intended for this condition. Suppose that 
at the site we have local terrain which, in equilibrium 
conditions, would have an exposure coefficient at height 
z of K z \ but there is, at a distance x km in the upwind 
direction, a change in the terrain. Upwind of the change 
the terrain is such that the normal equilibrium exposure 
coefficient would be K z2 . The effect of this change in terrain 
on the exposure coefficient at the site can be represented 
by adjusting K z \ by an increment AK, thus arriving at a 
corrected value K z for the site. 

K z = K zi + AK (Eq. C6-6) 

In this expression AK is calculated using 

K 10,1 



I Air | < \k z2 ~k z1 



(Eq. C6-7) 



where K\qj and K\o^ are > respectively, the local and 
upwind equilibrium values of exposure coefficient at 10 m 
height, and the function F A k(x), with x measured in 
kilometers, is given by 

F AK (x) = log l0 ( j) /log 10 (~) (Eq. C6-8) 



(Eq. C6-4) for x o < x < x. 



F&k(x) — 1 for x < xo 
F Ak {x) — for X\ < x 

The "starting" value of x is given by 



x - 10" 



-(7<ioj — ATio.a)"— 2.3 



(Eq. C6-9) 



The "finishing" value for x is given by x\ = 10 km for 
K\o.] < Kw,2 (wind going from smooth terrain 2 to rough 
terrain 1) or x\ = 100 km for K\o,\ > Kuu) (wind going 
from rough terrain 2 to smooth terrain 1). 

As an example, suppose the building is 20 m high 
in suburban surroundings (Exposure B) but the edge of 
the suburban terrain is 0.6 km upwind with open coun- 
try (Exposure C) beyond. We thus have x = 0.6 km and 
^io,i, ^10,2 anc * ^20,i. are 0.72, 1.0 and 0.88, respectively, 
(from Table 6.3). From Equation C6-8, F AK (x) is calcu- 
lated to be 0.36 and AK is calculated from Eq. 6-7 to 
be (1.00 - 0.72) x (0.88/0.72 x 0.36 - 0.124. Thus, from 
Eq. C6-6 the value of K z at 20 m height should be 
increased from its equilibrium value of 0.88 by an incre- 
ment of 0.124, bringing it up to 1.004. 

Note that in this case the simple rules in Section 6 
would require Exposure C be applied since the extent of 



282 



ASCE 7-02 



Exposure B roughness is less than 800 m, resulting in 
K20 — 1.16. The above interpolation method would enable 
a value of 1.004 to be used instead. In some cases, the 
interpolation method will give a higher exposure coefficient 
than the simple rules. In these cases, the simple rules 
can be used if desired as the differences are typically 
within the range of uncertainty resulting from estimation 
of roughness lengths. 

C6.5.7 Wind Speed-Up over Hills and Escarp- 
ments. As an aid to the designer, this Section was rewrit- 
ten in ASCE 7-98 to specify when topographic effects need 
to be applied to a particular structure rather than when they 
do not as in the previous version. In addition, the upwind 
distance to consider has been lengthened from 50 times to 
100 times the height of the topographic feature (100 H) 
and from 1 to 2 miles. In an effort to exclude situations 
where little or no topographic effect exists, condition (2) 
has been added to include the fact that the topographic 
feature should protrude significantly above (by a factor of 
2 or more) upwind terrain features before it becomes a 
factor. For example, if a significant upwind terrain fea- 
ture has a height of 35 feet above its base elevation and 
has a top elevation of 100 feet above mean sea level, then 
the topographic feature (hill, ridge, or escarpment) must 
have at least the H specified and extend to elevation 170 
mean sea level (100 ft + 2 x 35 ft) within the 2-mile radius 
specified. 

A recent wind-tunnel study [C6-81] and observation of 
actual wind damage has shown that the affected height H 
is less than previously specified. Accordingly, condition (5) 
was changed to 15 feet in Exposure C. 

Buildings sited on the upper half of an isolated hill 
or escarpment may experience significantly higher wind 
speeds than buildings situated on level ground. To account 
for these higher wind speeds, the velocity pressure exposure 
coefficients in Table 6-3 are multiplied by a topographic 
factor, K zt , defined in Eq. 6-15 of Section 6.5.10. The 
topographic feature (two-dimensional ridge or escarpment, 
or three-dimensional axi symmetrical hill) is described by 
two parameters, H and L/ ? . H is the height of the hill or 
difference in elevation between the crest and that of the 
upwind terrain. L h is the distance upwind of the crest to 
where the ground elevation is equal to half the height of 
the hill. K zt is determined from three multipliers, K\, K2, 
and K3, which are obtained from Figure 6-4, respectively. 
K] is related to the shape of the topographic feature and 
the maximum speed-up near the crest, K2 accounts for the 
reduction in speed-up with distance upwind or downwind 
of the crest, and K^ accounts for the reduction in speed-up 
with height above the local ground surface. 

The multipliers listed in Figure 6-4 are based on the 
assumption that the wind approaches the hill along the 
direction of maximum slope, causing the greatest speed- 
up near the crest. The average maximum upwind slope 
of the hill is approximately H/2L h , and measurements 



have shown that hills with slopes of less than about 0.10 
{H/Ljj < 0.20) are unlikely to produce significant speed- 
up of the wind. For values of H '/L/,. > 0.5, the speed-up 
effect is assumed to be independent of slope. The speed- 
up principally affects the mean wind speed rather than 
the amplitude of the turbulent fluctuations and this fact 
has been accounted for in the values of K\, K 2 , and ^3 
given in Figure 6-4. Therefore, values of K zt obtained 
from Figure 6-4 are intended for use with velocity pressure 
exposure coefficients, K^ and K z , which are based on 
gust speeds. 

It is not the intent of Section 6.5.7 to address the general 
case of wind flow over hilly or complex terrain for which 
engineering judgment, expert advice, or wind-tunnel tests 
as described in Section 6.6 may be required. Background 
material on topographic speed-up effects may be found in 
the literature [C6-18, C6-21, C6-56]. 

The designer is cautioned that, at present, the Standard 
contains no provision for vertical wind speed-up because 
of a topographic effect, even though this phenomenon is 
known to exist and can cause additional uplift on roofs. 
Additional research is required to quantify this effect before 
it can be incorporated into the Standard. 

C6.5.8 Gust Effect Factors. ASCE 7-02 contains a single 
gust effect factor of 0.85 for rigid buildings. As an option, 
the designer can incorporate specific features of the wind 
environment and building size to more accurately calcu- 
late a gust effect factor. One such procedure, previously 
contained in the commentary, is now located in the body 
of the Standard [C6-63, C6-64]. A suggested procedure is 
also included for calculating the gust effect factor for flex- 
ible structures. The rigid structure gust factor is typically 
0%-4% higher than in ASCE 7-95 and is 0%-10% lower 
than the simple, but conservative, value of 0.85 permitted in 
the Standard without calculation. The procedures for both 
rigid and flexible structures have been changed from the 
previous version to (1) keep the rigid gust factor calculation 
within a few percentages of the previous model, (2) provide 
a superior model for flexible structures which displays the 
peak factors gQ and g#, and (3) causes the flexible structure 
value to match the rigid structure as resonance is removed 
(an advantage not included in the previous version). A 
designer is free to use any other rational procedure in the 
approved literature, as stated in Section 6.5.8.3. 

The gust effect factor accounts for the loading effects in 
the along- wind direction due to wind turbulence structure 
interaction. It also accounts for along-wind loading effects 
due to dynamic amplification for flexible buildings and 
structures. It does not include allowances for across-wind 
loading effects, vortex shedding, instability due to galloping 
or flutter, or dynamic torsional effects. For structures 
susceptible to loading effects that are not accounted for 
in the gust effect factor, information should be obtained 
from recognized literature [C6-60-C6-65] or from wind 
tunnel tests. 



Minimum Design Loads for Buiidings and Other Structures 



283 



Along- Wind Response. Based on the preceding definition 
of the gust effect factor, predictions of along- wind response 
(e.g., maximum displacement, rms, and peak acceleration), 
can be made. These response components are needed 
for survivability and serviceability limit states. In the 
following, expressions for evaluating these along-wind 
response components are given. 



Maximum Along- Wind Displacement. The maximum 
along-wind displacement X mSLX (z) as a function of height 
above the ground surface is given by 



AZ) = 



<f>(z)pBhC fx V- 



2m j {2izn\) 2 



^KG 



(Eq. C6-10) 



where 0(z)=the fundamental model shape <p(z) = 
(z/h)^; £ = the mode exponent; p — air density; Cf X = 
mean along-wind force coefficient; ni\ ~ modal mass — 
fj ix{z)4> 2 (z)dz\ fJb{z) — mass per unit height: K = 
(\.(*5) a l(a + £ -h l);and VV is the 3-sec gust speed at height 
z. This can be evaluated by Vj = b(z/33) a V\ where V is 
the 3-sec gust speed in Exposure C at the reference height 
(obtained from Figure 6-1); b and a are given in Table 6-2. 



RMS Along-Wind Acceleration. The rms along-wind 
acceleration a^iz) as a function of height above the ground 
surface is given by 



cr?(z) = -^-^ ^^hKR (Eq. C6-11) 

m i 

where Vj is the mean hourly wind speed at height z, ft/sec 



k, = M-1 v 



where b and a are defined in Table 6-2. 

Maximum Along-Wind Acceleration. The maximum 
along-wind acceleration as a function of height above the 
ground surface is given by 

X m **(z) = gx<rx(z) (Eq.C6-12) 

0.5772 



g$ = v/21n(n,r) + 



y/ZMrTiT) 



where T — the length of time over which the minimum 
acceleration is computed, usually taken to be 3600 sec to 
represent 1 hour. 



Example. The following example is presented to illus- 
trate the calculation of the gust effect factor. Table C6-3 
uses the given information to obtain values from Table 6-2, 



Table C6-4 presents the calculated values. Table C6-5 sum- 
marizes the calculated displacements and accelerations as a 
function of the height, z. 



Given Values. 

Basic wind speed at reference height in Exposure 

C= 90mph 
Type of Exposure = A (from ASCE 7-98) 
Building height h - 600 ft 
Building width B = 100 ft 
Building depth L = 100 ft 
Building natural frequency ri\ — 0.2 Hz 
Damping ratio = 0.01 
C fx = 1.3 

Mode exponent = 1 .0 

Building density = 12 lb/ft 3 = 0.3727 slugs/ft 3 
Air density = 0.0024 slugs/ft 3 

C6.5.9 Enclosure Classifications. The magnitude and 
sense of internal pressure is dependent upon the magnitude 
and location of openings around the building envelope 
with respect to a given wind direction. Accordingly, the 
Standard requires that a determination be made of the 
amount of openings in the envelope in order to assess 
enclosure classification (enclosed, partially enclosed, or 
open). "Openings" are specifically defined in this version of 
the Standard as "apertures or holes in the building envelope 
which allow air to flow through the building envelope 
and which are designed as "open" during design winds." 
Examples include doors, operable windows, air intake 
exhausts for air conditioning and/or ventilation systems, 
gaps around doors, deliberate gaps in cladding and flexible 
and operable louvers. Once the enclosure classification 
is known, the designer enters Figure 6-5 to select the 
appropriate internal pressure coefficient. 

This version of the Standard has four definitions appli- 
cable to enclosure: "wind-borne debris regions," "glazing," 
"impact-resistant glazing," and "impact-resistant cover- 
ing." "Wind-borne debris regions" are defined to alert the 
designer to areas requiring consideration of missile impact 
design and potential openings in the building envelope. 
"Glazing" is defined as "any glass or transparent or translu- 
cent plastic sheet used in windows, doors, skylights, or 
curtain walls." "Impact-resistant glazing" is specifically 
defined as "glazing which has been shown by testing in 
accordance with ASTM E 1886 [C6-70] and ASTM E 1996 
[C6-71] or other approved test methods to withstand the 
impact of wind-borne missiles likely to be generated in 
wind-borne debris regions during design winds." "Impact- 
resistant covering" over glazing can be shutters or screens 
designed for wind-borne debris impact. Impact resistance 
can now be tested using the test method specified in 
ASTM E 1886 [C6-70], with missiles, impact speeds, and 
pass/fail criteria specified in ASTM E 1996 [C6-71]. Other 



284 



ASCE 7-02 



approved test methods are acceptable. Origins of missile 
impact provisions contained in these Standards are summa- 
rized in References [C6-72 and C6-80]. 

Attention is made to Section 6.5.9.3, which requires 
glazing in Category II, III, and IV buildings in wind-borne 
debris regions to be protected with an impact-resistant cov- 
ering or be impact resistant. For Category II and III build- 
ings (other than health care, jails and detention facilities, 
and power-generating and other public utility facilities), an 
exception allows unprotected glazing, provided the glazing 
is assumed to be openings in determining the building's 
exposure classification. The option of unprotected glaz- 
ing for Category III health care, jails and detention facil- 
ities, power-generating and other public utility facilities, 
and Category IV buildings was eliminated in this edition 
of the Standard because it is important for these facili- 
ties to remain operational during and after design wind- 
storm events. 

Prior to this edition of the Standard, glazing in the 
lower 60 ft (18.3 m) of Category II, III, or IV buildings 
sited in wind-borne debris regions was required to be 
protected with an impact-resistant covering, or be impact- 
resistant, or the glazing was to be assumed to be openings. 
Recognizing that glazing higher than 60 ft (18.3 m) above 
grade may be broken by wind-borne debris when a debris 
source, is present, a new provision was added. With this 
new provision, aggregate surface roofs on buildings within 
1500 ft of the new building need to be evaluated. For 
example, loose roof aggregate that is not protected by an 
extremely high parapet should be considered as a debris 
source. Accordingly, the glazing in the new building, from 
30 ft (9.2 m) above the source building to grade would 
need to be protected or assumed to be open. If loose roof 
aggregate is proposed for the new building, it too should 
be considered as a debris source because aggregate can 
be blown off the roof and be propelled into glazing on 
the leeward side of the building. Although other types of 
wind-borne debris can impact glazing higher than 60 ft 
above grade, at these high elevations, loose roof aggregate 
has been the predominant debris source in previous wind 
events. The requirement for protection 30 ft (9.1 m) above 
the debris source is to account for debris that can be lifted 
during flight. The following References provide further 
information regarding debris damage to glazing: [C6-72, 
C6-97-C6-100]. 

Levels of impact resistance specified 
in ASTM E 1996-1999* 



Building 
Classification 


Category II & III 

(Note 1) 


Category III & IV 

(Note 2) 


Glazing 
Height 


<30 ft 

(9.1 m) 


>30 ft. 

(9.1 m) 


<30 ft. 
(9.1 m) 


>30 ft. 

(9.1 m) 


Wind Zone 1 
Wind Zone 2 
Wind Zone 3 


Missile B 
Missile B 
Missile C 


Missile A 
Missile A 
Missile A 


Missile C 
Missile C 
Missile D 


Missile C 
Missile C 
Missile C 


* Reprinted with permission from ASTM. 



Wind Zone 1: Wind-borne debris region where basic 
wind speed is greater than or equal to 110 mph but less 
than 120 mph and Hawaii. 

Wind Zone 2: Wind-borne debris region where basic 
wind speed is greater than or equal to 1 20 mph but less than 
130 mph at greater than 1 mile (1.6 km) of the coastline 
(Note 3). 

Wind Zone 3: Wind-borne debris region where basic 
wind speed is greater than or equal to 130 mph, or where 
the basic wind speed is greater than or equal to 120 mph 
and within 1 mile (1.6 km) of the coastline (Note 3). 

Note 1. Category III other than health care, jails and 
detention facilities, power-generating and other public util- 
ity facilities. 

Note 2. Category III health care, jails and detention 
facilities, power-generating and other public utility facil- 
ities only. 

Note 3. The coastline shall be measured from the mean 
high waterline. 

Note 4. For porous shutter assemblies that contain open- 
ings greater than 3/16 in. (5 mm) projected horizontally, 
missile A shall also be used where missile B, C, or D 
are specified. 



Missile levels specified 


in ASTM E 




1996-1999 


* 


Missile 






Level 


Missile 


Impact Speed 


Missile A 


2 g ± 5% steel ball 


130 ft/sec (39.6 m/s) 


Missile B 


4.5 lb ± 0.25 lb 
(2050 g± 100 g) 
2x4 lumber 
4' _ o" ± 4" 
(1.2 m± 100 mm) 
long 


40 ft/sec (12.2 m/s) 


Missile C 


9.0 lb ± 0.25 lb 
(4100 g± 100 g) 
2x4 lumber 

8' - 0" ± 4" 

(2.4 m± 100 mm) 

long 


50 ft/sec (15.3 m/s) 


Missile D 


9.0 lb ±0.25 lb 
(4100 g± 100 g) 
2x4 lumber 

8 / - 0" ± 4" 

(2.4 m± 100 mm) 

long 


80 ft/sec (24.4 m/s) 


* Reprinted 


with permission from 


ASTM. 



C6.5.10 Velocity Pressure. The basic wind speed is con- 
verted to a velocity pressure q z in pounds per square foot 
(newtons/m 2 ) at height z by the use of Eq. 6-15. 



Minimum Design Loads for Buildings and Other Structures 



285 



The constant 0.00256 (or 0.613 in SI) reflects the 
mass density of air for the standard atmosphere, i.e., 
temperature of 59 °F (15 °C) and sea level pressure of 
29.92 inches of mercury (101.325 kPa), and dimensions 
associated with wind speed in mph (m/s). The constant is 
obtained as follows: 

constant = l/2[(0.0765 lb/ft 3 )/(32.2 ft/s 2 )] 

x [(mi/h)(5280 ft/mi) 

x (1 h/3600 s)] 2 
= 0.00256 
constants 1/2[(1.225 kg/m 3 )/(9.81 m/s 2 )] 

x [(m/s)] 2 [9.81 N/kg]= 0.613 

The numerical constant of 0.00256 should be used except 
where sufficient weather data are available to justify a 
different value of this constant for a specific design 
application. The mass density of air will vary as a function 
of altitude, latitude, temperature, weather, and season. 
Average and extreme values of air density are given in 
Table C6-6. 

C6.5.11 Pressure and Force Coefficients. The pressure 
and force coefficients provided in Figures 6-6 through 6-22 
have been assembled from the latest boundary-layer wind- 
tunnel and full-scale tests and from previously available 
literature. Since the boundary-layer wind-tunnel results 
were obtained for specific types of building such as low- 
or high-rise buildings and buildings having specific types 
of structural framing systems, the designer is cautioned 
against indiscriminate interchange of values among the 
figures and tables. 

Loads on Main Wind Force-Resisting Systems. 

Figures 6-6 and 6-10. The pressure coefficients for 
main wind force-resisting systems are separated into 
two categories: 

1. Buildings of all heights (Figure 6-6); and 

2. Low-rise buildings having a height less than or equal 
to 60 ft (18 m) (Figure 6-10). 

In generating these coefficients, two distinctly different 
approaches were used. For the pressure coefficients given 
in Figure 6-6, the more traditional approach was followed 
and the pressure coefficients reflect the actual loading on 
each surface of the building as a function of wind direction; 
namely, winds perpendicular or parallel to the ridge line. 

Observations in wind tunnel tests show that areas of very 
low negative pressure and even slightly positive pressure 
can occur in all roof structures, particularly as the distance 



from the windward edge increases and the wind streams 
reattach to the surface. These pressures can occur even 
for relatively flat or low-slope roof structures. Experience 
and judgment from wind-tunnel studies have been used to 
specify either zero or slightly negative pressures (—0.1.8) 
depending on the negative pressure coefficient. These new 
values require the designer to consider a zero or slightly 
positive net wind pressure in the load combinations of 
Section 2. 

For low-rise buildings having a height less than or equal 
to 60 ft (18 m), however, the values of GC p f represent 
"pseudo" loading conditions which, when applied to the 
building, envelope the desired structural actions (bending 
moment, shear, thrust) independent of wind direction. To 
capture all appropriate structural actions, the building must 
be designed for all wind directions by considering in 
turn each corner of the building as the reference corner 
shown in the sketches of Figure 6-10. In ASCE 7-02, these 
sketches were modified in an attempt to clarify the proper 
application of the patterns. At each corner, two load patterns 
are applied, one for each MWFRS direction. The proper 
orientation of the load pattern is with the end zone strip 
parallel to the MWFRS direction. The end zone creates 
the required structural actions in the end frame or bracing. 
Note also that for all roof slopes, all 8 load cases must be 
considered individually in order to determine the critical 
loading for a given structural assemblage or component 
thereof. Special attention should be given roof members 
such as trusses, which meet the definition of MWFRS, 
but are not part of the lateral resisting system. When such 
members span at least from the eave to the ridge or support 
members spanning at least from eave to ridge, they are not 
required to be designed for the higher end zone loads under 
MWFRS. The interior zone loads should be applied. This is 
due to the enveloped nature of the loads for roof members. 

To develop the appropriate "pseudo" values of GC p f, 
investigators at the University of Western Ontario [C6-11] 
used an approach which consisted essentially of permitting 
the building model to rotate in the wind tunnel through a full 
360 degrees while simultaneously monitoring the loading 
conditions on each of the surfaces (see Figure C6-7). Both 
Exposures B and C were considered. Using influence 
coefficients for rigid frames, it was possible to spatially 
average and time average the surface pressures to ascertain 
the maximum induced external force components to be 
resisted. More specifically, the following structural actions 
were evaluated: 

1 . total uplift 

2. total horizontal shear 

3. bending moment at knees (2-hinged frame) 

4. bending moment at knees (3-hinged frame), and 

5. bending moment at ridge (2-hinged frame) 

The next step involved developing sets of "pseudo" 
pressure coefficients to generate loading conditions which 



286 



ASCE 7-02 



would envelope the maximum induced force components 
to be resisted for all possible wind directions and expo- 
sures. Note, for example, that the wind azimuth producing 
the maximum bending moment at the knee would not nec- 
essarily produce the maximum total uplift. The maximum 
induced external force components determined for each of 
the above five categories were used to develop the coef- 
ficients. The end result was a set of coefficients which 
represent fictitious loading conditions, but which conser- 
vatively envelope the maximum induced force components 
(bending moment, shear, and thrust) to be resisted, inde- 
pendent of wind direction. 

The original set of coefficients was generated for the 
framing of conventional pre-engineered buildings, i.e., 
single story moment-resisting frames in one of the principal 
directions and bracing in the other principal direction. 
The approach was later extended to single story moment- 
resisting frames with interior columns [C6-19]. 

Subsequent wind-tunnel studies [C6-69] have shown 
that the GC P f values of Figure 6-10 are also applicable 
to low-rise buildings with structural systems other 
than moment-resisting frames. That work examined the 
instantaneous wind pressures on a low-rise building with 
a 4:12 pitched gable roof and the resulting wind-induced 
forces on its main wind force-resisting system. Two 
different main wind force-resisting systems were evaluated. 
One consisted of shear walls and roof trusses at different 
spacings. The other had moment-resisting frames in one 
direction, positioned at the same spacings as the roof 
trusses, and diagonal wind bracing in the other direction. 
Wind-tunnel tests were conducted for both Exposures B 
and C. The findings of this study showed that the GC p f 
values of Figure 6-10 provided satisfactory estimates of 
the wind forces for both types of structural systems. 
This work confirms the validity of Figure 6-10, which 
reflects the combined action of wind pressures on different 
external surfaces of a building and thus take advantage of 
spatial averaging. 

In the original wind-tunnel experiments, both B and C 
exposure terrains were checked. In these early experiments, 
B exposure did not include nearby buildings. In general, 
the force components, bending moments, and so on, were 
found comparable in both exposures, although GC P f values 
associated with Exposure B terrain would be higher than 
that for Exposure C terrain because of reduced velocity 
pressure in Exposure B terrain. The GC P f values given 
in Figures 6-10 through 6-15 are derived from wind- 
tunnel studies modeled with Exposure C terrain. However, 
they may also be used in other exposures when the 
velocity pressure representing the appropriate exposure 
is used. 

In recent comprehensive wind-tunnel studies conducted 
by [C6-66] at the University of Western Ontario, it was 
determined that when low buildings (h < 60 ft) are embed- 
ded in suburban terrain (Exposure B, which included 
nearby buildings), the pressures in most cases are lower 



than those currently used in existing standards and codes, 
although the values show a very large scatter because of 
high turbulence and many variables. The results seem to 
indicate that some reduction in pressures for buildings 
located in Exposure B is justified. The Task Committee 
on Wind Loads believes it is desirable to design buildings 
for the exposure conditions consistent with the exposure 
designations defined in the Standard. In the case of low 
buildings, the effect of the increased intensity of turbulence 
in rougher terrain (i.e., Exposure A or B versus C) increases 
the local pressure coefficients. In ASCE 7-95, this effect 
was accounted for by allowing the designer of a building 
situated in Exposure A or B to use the loads calculated as if 
the building were located in Exposure C, but to reduce the 
loads by 15%. In ASCE 7-98, the effect of the increased tur- 
bulence intensity on the loads is treated with the truncated 
profile. Using this approach, the actual building exposure 
is used and the profile truncation corrects for the underes- 
timate in the loads that would be obtained otherwise. The 
resulting wind loads on components and cladding obtained 
using this approach are much closer to the true values than 
those obtained using Exposure C loads combined with a 
15% reduction in the resulting pressures. 

Figure 6-10 is most appropriate for low buildings with 
width greater than twice their height and a mean roof 
height that does not exceed 33 ft (10 m). The original 
database included low buildings with width no greater than 
5 times their eave height, and eave height did not exceed 
33 ft (10 m). In the absence of more appropriate data, 
Figure 6-10 may also be used for buildings with mean roof 
height which does not exceed the least horizontal dimension 
and is less than or equal to 60 ft (18 m). Beyond these 
extended limits, Figure 6-6 should be used. 

All the research used to develop and refine the low- 
rise building method for MWFRS loads was done on gable 
roofed buildings. In the absence of research on hip roofed 
buildings, the committee has developed a rational method 
of applying Figure 6-10 to hip roofs based on its collective 
experience, intuition, and judgment. This suggested method 
is presented in Figure C6-8. 

Recent research [C6-93, C6-94] indicates that in the past 
the low-rise method underestimated the amount of torsion 
caused by wind loads. In ASCE 7-02, Note 5 was added 
to Figure 6-10 to account for this torsional effect. The 
reduction in loading on only 50% of the building results 
in a torsional load case without an increase in the predicted 
base shear for the building. The provision will have little 
or no effect on the design of main wind force-resisting 
systems that have well-distributed resistance. However, 
it will impact the design of systems with centralized 
resistance, such as a single core in the center of the building. 
An illustration of the intent of the note on 2 of the 8 load 
patterns is shown in Figure 6-10. All 8 patterns should be 
modified in this way as a separate set of load conditions in 
addition to the 8 basic patterns. 



Minimum Design Loads for Buildings and Other Structures 



287 



Internal pressure coefficients (GC p i) to be used for 
loads on main wind force-resisting systems are given in 
Figure 6-5. The internal pressure load can be critical in 1- 
story moment-resisting frames and in the top story of a 
building where the main wind force-resisting system con- 
sists of moment-resisting frames. Loading cases with pos- 
itive and negative internal pressures should be considered. 
The internal pressure load cancels out in the determination 
of total lateral load and base shear. The designer can use 
judgment in the use of internal pressure loading for the 
main wind force-resisting system of high-rise buildings. 

Figure 6-7. Frame loads on dome roofs are adapted from 
the proposed Eurocode [C6-102]. The loads are based on 
data obtained in a modeled atmospheric boundary-layer 
flow which does not fully comply with requirements for 
wind-tunnel testing specified in this Standard [C6-101]. 
Loads for three domes (h D /D = 0.5, f/D = 0.5), (h D /D = 
0, f/D = 0.5), (h D /D == 0, f/D = 0.33) are roughly con- 
sistent with data of Taylor [C6-103], who used an atmo- 
spheric boundary layer as required in this Standard. Two 
load cases are defined, one of which has a linear vari- 
ation of pressure from A to B as in the Eurocode [C6- 
102] and one in which the pressure at A is held constant 
from to 25 degrees; these two cases are based on com- 
parison of the Eurocode provisions of Taylor [C6-103]. 
Case A (the Eurocode calculation) is necessary in many 
cases to define maximum uplift. Case B is necessary to 
properly define positive pressures for some cases (which 
cannot be isolated with current information) and which 
result in maximum base shear. For domes larger than 200 ft 
diameter, the designer should consider use of Method 3. 
Resonant response is not considered in these provisions; 
Method 3 should be used to consider resonant response. 
Local bending moments in the dome shell may be larger 
than predicted by this method due to the difference between 
instantaneous local pressure distributions and that predicted 
by Figure 6-7. If the dome is supported on vertical walls 
directly below, it is appropriate to consider the walls as a 
"chimney" using Figure 6-19. 



building model was permitted to rotate in the wind-tunnel 
through 360 degrees. As the induced localized pressures 
may also vary widely as a function of the specific location 
on the building, height above ground level, exposure, 
and more importantly, local geometric discontinuities and 
location of the element relative to the boundaries in the 
building surfaces (walls, roof lines), these factors were 
also enveloped in the wind-tunnel tests. Thus, for the 
pressure coefficients given in Figures 6-11 through 6-15, 
the directionality of the wind and influence of exposure 
have been removed and the surfaces of the building "zoned" 
to reflect an envelope of the peak pressures possible for a 
given design application. 

As indicated in the discussion for Figure 6-10, the wind- 
tunnel experiments checked both B and C exposure ter- 
rains. Basically, GC P values associated with Exposure B 
terrain would be higher than those for Exposure C ter- 
rain because of reduced velocity pressure in Exposure B 
terrain. The GC P values given in Figures 6-11 through 6- 
15 are associated with Exposure C terrain as obtained in 
the wind tunnel. However, they may be also used for any 
exposure when the correct velocity pressure representing 
the appropriate exposure is used. (See commentary dis- 
cussion in Section C6. 5. 11 under Loads on Main Wind 
Force-Resisting Systems.) 

The wind-tunnel studies conducted by [C6-66] deter- 
mined that when low buildings (h < 60 ft) are embedded 
in suburban terrain (Exposure B), the pressures on com- 
ponents and cladding in most cases are lower than those 
currently used in the standards and codes, although the 
values show a very large scatter because of high turbu- 
lence and many variables. The results seem to indicate that 
some reduction in pressures for components and cladding 
of buildings located in Exposure B is justified. 

The pressure coefficients given in Figure 6-17 for build- 
ings with mean height greater than 60 ft were developed 
following a similar approach, but the influence of expo- 
sure was not enveloped [C6-42]. Therefore, Exposure Cat- 
egories B, C, or D may be used with the values of GC P in 
Figure 6-8 as appropriate. 



Loads on Components and Cladding. In developing 
the set of pressure coefficients applicable for the design 
of components and cladding as given in Figures 6-11 
through 6-15, an envelope approach was followed but 
using different methods than for the main wind force- 
resisting systems of Figure 6-10. Because of the small 
effective area which may be involved in the design of a 
particular component (consider, for example, the effective 
area associated with the design of a fastener), the point- 
wise pressure fluctuations may be highly correlated over 
the effective area of interest. Consider the local purlin 
loads shown in Figure C6-4. The approach involved spatial 
averaging and time averaging of the point pressures over 
the effective area transmitting loads to the purlin while the 



Figure 6-11 The pressure coefficient values provided in 
this figure are to be used for buildings with a mean 
roof height of 60 ft (18 m) or less. The values were 
obtained from wind-tunnel tests conducted at the University 
of Western Ontario [C6-10, C6-11], at the James Cook 
University of North Queensland [C6-6], and at Concordia 
University [C6-40, C6-41, C6-44, C6-45, C6-47]. These 
coefficients have been refined to reflect results of full-scale 
tests conducted by the National Bureau of Standards [C6- 
22] and the Building Research Station, England [C6-14]. 
Pressure coefficients for hemispherical domes on ground 
or on cylindrical structures have been reported [C6-52]. 
Some of the characteristics of the values in the figure are 
as follows: 



288 



ASCE 7-02 



1. The values are combined values of GC P \ the 
gust effect factors from these values should not 
be separated. 

2. The velocity pressure q^ evaluated at mean roof 
height should be used with all values of GC P . 

3. The values provided in the figure represent the 
upper bounds of the most severe values for any 
wind direction. The reduced probability that the 
design wind speed may not occur in the particular 
direction for which the worst pressure coefficient is 
recorded has not been included in the values shown 
in the figure. 

4. The wind-tunnel values, as measured, were based on 
the mean hourly wind speed. The values provided in 
the figures are the measured values divided by (1.53) 2 
(see Figure C6-2) to reflect the reduced pressure coef- 
ficient values associated with a 3-second gust speed. 

Each component and cladding element should be 
designed for the maximum positive and negative pressures 
(including applicable internal pressures) acting on it. The 
pressure coefficient values should be determined for each 
component and cladding element on the basis of its 
location on the building and the effective area for the 
element. As recent research has shown [C6-41, C6-43], the 
pressure coefficients provided generally apply to facades 
with architectural features such as balconies, ribs, and 
various facade textures. 

More recent studies [C6-104, C6-105, C6-106] have led 
to updating the roof slope range and the values of GC p 
included in ASCE 7-02. 

Figures 6-13 and 6-14A. These figures present values of 
GC P for the design of roof components and cladding for 
buildings with multispan gable roofs and buildings with 
monoslope roofs. The coefficients are based on wind-tunnel 
studies reported by [C6-46, C6-47, C6-51]. 

Figure 6-14B. The values of GC p in this figure are for the 
design of roof components and cladding for buildings with 
sawtooth roofs and mean roof height, h, less than or equal to 
60 ft (18 m). Note that the coefficients for corner zones on 
segment A differ from those coefficients for corner zones 
on the segments designated as B, C, and D. Also, when 
the roof angle is less than or equal to 10 degrees, values 
of GC p for regular gables roofs (Figure 6-1 IB) are to be 
used. The coefficients included in Figure 6-14B are based 
on wind-tunnel studies reported by [C6-35]. 

Figure 6-17. The pressure coefficients shown in this figure 
have been revised to reflect the results obtained from 
comprehensive wind-tunnel studies carried out by [C6- 
42]. In general, the loads resulting from these coefficients 
are lower than those required by ASCE 7-93. However, 



the area averaging effect for roofs is less pronounced 
when compared with the requirements of ASCE 7-93. The 
availability of more comprehensive wind-tunnel data has 
also allowed a simplification of the zoning for pressure 
coefficients; flat roofs are now divided into three zones, 
and walls are represented by two zones. 

The external pressure coefficients and zones given in 
Figure 6-17 were established by wind-tunnel tests on iso- 
lated "box-like" buildings [C6-2, C6-31]. Boundary-layer 
wind-tunnel tests on high-rise buildings (mostly in down- 
town city centers) show that variations in pressure coef- 
ficients and the distribution of pressure on the different 
building facades are obtained [C6-53]. These variations 
are due to building geometry, low attached buildings, non- 
rectangular cross sections, setbacks, and sloping surfaces. 
In addition, surrounding buildings contribute to the varia- 
tions in pressure. Wind-tunnel tests indicate that pressure 
coefficients are not distributed symmetrically and can give 
rise to torsional wind loading on the building. 

Boundary-layer wind-tunnel tests that include modeling 
of surrounding buildings permit the establishment of more 
exact magnitudes and distributions of GC P for buildings 
that are not isolated or "box-like" in shape. 

Figure 6-16. This figure for cladding pressures on dome 
roofs is based on Taylor [C6-103]. Negative pressures are 
to be applied to the entire surface, since they apply along 
the full arc, which is perpendicular to the wind direction 
and which passes through the top of the dome. Users 
are cautioned that only 3 shapes were available to define 
values in this figure (h D /D = 0.5, f/D = 0.5; h D ID = 0.0, 
f/D = 0.5; h D ID = 0.0, f/d = 0.33). 

Figure 6-8 and Figures 6-18 through 6-22. With the 
exception of Figure 6-22, the pressure and force coefficient 
values in these tables are unchanged from ANSI A58.1- 
1972 and 1982, and ASCE 7-88 and 7-93. The coefficients 
specified in these tables are based on wind-tunnel tests 
conducted under conditions of uniform flow and low 
turbulence, and their validity in turbulent boundary layer 
flows has yet to be completely established. Additional 
pressure coefficients for conditions not specified herein may 
be found in References [C6-3 and C6-36]. With regard to 
Figure 6-19, local maximum and minimum peak pressure 
coefficients for cylindrical structures with h/D < 2 are 
GC P = 1.1 and GC P = -1.1, respectively, for Reynolds 
numbers ranging from 1.1 x 10 5 to 3.1 x 10 5 [C6-23]. The 
latter results have been obtained under correctly simulated 
boundary layer flow conditions. 

With regard to Figure 6-22, the force coefficients are 
a refinement of the coefficients specified in ANSI A58.1- 
1.982 and in ASCE 7-93. The force coefficients specified 
are offered as a simplified procedure that may be used for 
trussed towers and are consistent with force coefficients 
given in ANSI/EIA/TIA-222-E-1991, Structural Standards 



Minimum Design Loads for Buildings and Other Structures 



289 



for Steel Antenna Towers and Antenna Supporting Struc- 
tures, and force coefficients recommended by Working 
Group No. 4 (Recommendations for Guyed Masts), Interna- 
tional Association for Shell and Spatial Structures (1981). 

It is not the intent of the Standard to exclude the use 
of other recognized literature for the design of special 
structures such as transmission and telecommunications 
towers. Recommendations for wind loads on tower guys 
are not provided as in previous editions of the Standard. 
Recognized literature should be referenced for the design 
of these special structures as is noted in C6.4.2.1. For the 
design of flagpoles, see ANSI/NAAMM FP1001-97, 4th 
Ed., Guide Specifications for Design of Metal Flagpoles. 

ASCE 7-02 has been modified to explicitly require the 
use of Figure 6-19 for the determination of the wind load 
on equipment located on a rooftop. Because there is a lack 
of research to provide better guidance for loads on rooftop 
equipment, this change was made based on the consensus 
opinion of the Committee. Because of the relatively small 
size of the equipment it is believed that the gust effect factor 
will be higher than 0.85; however, no research presently 
exists upon which to base a recommendation. Use of a gust 
effect factor of 1 . 1 or higher should be considered based on 
observations in a recent wind-tunnel study reported to the 
Task Committee on Wind Loads. Eq. 6-4 may be used as a 
guide in determining the gust effect factor. Caution should 
also be exercised in the positioning of the equipment on 
the roof. If rooftop equipment is located, either in whole 
or in part, in the higher pressure zones near a roofs edge, 
consideration should be given to increasing the wind load. 

C6.5.11.1 Internal Pressure Coefficients. The internal 
pressure coefficient values in Figure 6-5 were obtained 
from wind-tunnel tests [C6-38] and full-scale data [C6-59]. 
Even though the wind-tunnel tests were conducted primarily 
for low-rise buildings, the internal pressure coefficient 
values are assumed to be valid for buildings of any height. 
The values GC pl =+0.18 and -0.18 are for enclosed 
buildings. It is assumed that the building has no dominant 
opening or openings and that the small leakage paths 
that do exist are essentially uniformly distributed over the 
building's envelope. The internal pressure coefficient values 
for partially enclosed buildings assume that the building 
has a dominant opening or openings. For such a building, 
the internal pressure is dictated by the exterior pressure at 
the opening and is typically increased substantially as a 
result. Net loads, i.e., the combination of the internal and 
exterior pressures, are therefore also significantly increased 
on the building surfaces that do not contain the opening. 
Therefore, higher GC pi values of +0.55 and -0.55 are 
applicable to this case. These values include a reduction 
factor to account for the lack of perfect correlation between 
the internal pressure and the external pressures on the 
building surfaces not containing the opening [C6-82] [C6- 
83]. Taken in isolation, the internal pressure coefficients 



can reach values of ±0.8, (or possibly even higher on the 
negative side). 

For partially enclosed buildings containing a large unpar- 
titioned space, the response time of the internal pressure is 
increased and this reduces the ability of the internal pressure 
to respond to rapid changes in pressure at an opening. The 
gust factor applicable to the internal pressure is therefore 
reduced. Eq. 6-14, which is based on References [C6-84 
and C6-85] is provided as a means of adjusting the gust 
factor for this effect on structures with large internal spaces 
such as stadiums and arenas. 

Glazing in the bottom 60 ft of buildings that are sited 
in hurricane-prone regions that is not impact-resistant glaz- 
ing or is not protected by impact-resistant coverings should 
be treated as openings. Because of the nature of hurricane 
winds [C6-27], glazing in buildings sited in hurricane areas 
is very vulnerable to breakage from missiles, unless the 
glazing can withstand reasonable missile loads and subse- 
quent wind loading, or the glazing is protected by suitable 
shutters. Glazing above 60 ft (18 m) is also somewhat vul- 
nerable to missile damage, but because of the greater height, 
this glazing is typically significantly less vulnerable to dam- 
age than glazing at lower levels. When glazing is breached 
by missiles, development of high internal pressure results, 
which can overload the cladding or structure if the higher 
pressure was not accounted for in the design. Breaching 
of glazing can also result in a significant amount of water 
infiltration, which typically results in considerable damage 
to the building and its contents [C6-33, C6-49, C6-50]. 

If the option of designing for higher internal pressure 
(versus designing glazing protection) is selected, it should 
be realized that if glazing is breached, significant dam- 
age from overpressurization to interior partitions and ceil- 
ings is likely. The influence of compartmentation on the 
distribution of increased internal pressure has not been 
researched. If the space behind breached glazing is sep- 
arated from the remainder of the building by a sufficiently 
strong and reasonably air-tight compartment, the increased 
internal pressure would likely be confined to that compart- 
ment. However, if the compartment is breached (e.g., by 
an open corridor door, or by collapse of the compartment 
wall), the increased internal pressure will spread beyond 
the initial compartment quite rapidly. The next compart- 
ment may contain the higher pressure, or it too could be 
breached, thereby allowing the high internal pressure to 
continue to propagate. 

Because of the great amount of air leakage that often 
occurs at large hangar doors, designers of hangars should 
consider utilizing the internal pressure coefficients for 
partially enclosed buildings in Figure 6-5. 

C6.5.11.5 Parapets. Previous versions of the Standard 
have had no provisions for the design of parapets, although 
the companion "Guide" [C6-87] has shown a methodology. 
The problem has been the lack of direct research in this 
area on which to base provisions. Research has yet to 



290 



ASCE 7-02 



be performed, but the Committee thought that a rational 
method based on its collective experience, intuition, and 
judgment was needed, considering the large number of 
buildings with parapets. 

The methodology chosen assumes that parapet pressures 
are a combination of wall and roof pressures, depending on 
the location of the parapet, and the direction of the wind, 
see Figure C6-9. The windward parapet should receive the 
positive wall pressure to the front surface (exterior side 
of the building) and the negative roof edge zone pressure 
to the back surface (roof side). This concept is based 
on the idea that the zone of suction caused by the wind 
stream separation at the roof eave moves up to the top of 
the parapet when one is present. Thus the same suction 
which acts on the roof edge will also act on the back of 
the parapet. 

The leeward parapet would receive the positive wall 
pressure on the back surface (roof side) with the negative 
wall pressure on the front surface (exterior side of building). 
There should be no reduction in the positive wall pressure 
to the leeward due to shielding by the windward parapet, 
since typically, they are too far apart to experience this 
effect. Since all parapets would be designed for all wind 
directions, each parapet would in turn be the windward and 
leeward parapet and be designed for both sets of pressures. 

For the design of the main wind force-resisting system, 
the pressures used describe the contribution of the parapet 
to the overall wind loads on that system. A question 
arises whether to use the frame loads from MWFRS or 
the local loads from Components and Cladding. Both 
were studied using Figures 6-6 and 6-11. The use of 
Figure 6-10 coefficients would not have been appropriate 
since they are "pseudo-pressures" (see commentary on low- 
rise buildings). The results showed that the upper end 
of the range of frame loads match fairly closely with 
the lower end of the range of component loads. The 
judgment was made to use the upper end of the frame 
loads to determine the MWFRS coefficients used in the 
Standard. For simplicity, the front and back pressures on 
the parapet were combined into one coefficient for MWFRS 
design. The designer should not typically need the separate 
front and back pressures for MWFRS design. The internal 
pressures inside the parapet cancel out of the combined 
coefficient. The summation of these external and internal, 
front and back pressure coefficients is a new term GC pn , 
the main wind force-resisting system parapet combined net 
pressure coefficient. 

For the design of the components and cladding a similar 
approach was used. However, it is not possible to simplify 
the coefficients as much due to the increased complexity 
of the components and cladding pressure coefficients. In 
addition, the front and back pressures cannot necessarily 
be combined since the designer may be designing separate 
elements on each face of the parapet. The internal pressure 
is needed to account for net pressures on each surface. The 
new provisions guide the designer to the correct GC P mid 



velocity pressure to use for each surface as illustrated in 
Figure C6-9. 

Interior walls which protrude through the roof, such as 
party walls and fire walls, should be designed as windward 
parapets for both MWFRS and components and cladding. 

The internal pressure that may be present inside a parapet 
is highly dependent on the porosity of the parapet envelope. 
In other words, it depends on the likelihood of the wall 
surface materials to leak air pressure into the internal 
cavities of the parapet. For solid parapets such as concrete 
or masonry, the internal pressure is zero, since there is no 
internal cavity. Certain wall materials may be impervious to 
air leakage, and as such have little or no internal pressure or 
suction, so using the value of GC pi for an enclosed building 
may be appropriate. However, certain materials and systems 
used to construct parapets containing cavities are more 
porous, thus justifying the use of the GC pi values for 
partially enclosed buildings, or higher. Another factor in the 
internal pressure determination is whether the parapet cavity 
connects to the internal space of the building, allowing the 
building's internal pressure to propagate into the parapet. 

C6.5.12 Design Wind Loads on Buildings. The Standard 
provides specific wind pressure equations for both the main 
wind force-resisting systems and components and cladding. 
In Eqs. 6-17, 6-19, and 6-23 a new velocity pressure 
term "q" appears that is defined as the "velocity pressure 
for internal pressure determination." The positive internal 
pressure is dictated by the positive exterior pressure on 
the windward face at the point where there is an opening. 
The positive exterior pressure at the opening is governed 
by the value of q at the level of the opening, not q^. 
Therefore, the old provision which used q\ x as the velocity 
pressure is not in accord with the physics of the situation. 
For low buildings this does not make much difference, but 
for the example of a 300-ft tall building in Exposure B 
with a highest opening at 60 ft, the difference between 
#300 and q^ represents a 59% increase in internal pressure. 
This is unrealistic and represents an unnecessary degree 
of conservatism. Accordingly, qi = q z for positive internal 
pressure evaluation in partially enclosed buildings where 
height z is defined as the level of the highest opening in 
the building that could affect the positive internal pressure. 
For buildings sited in wind-borne debris regions, glazing 
that is not impact resistant or protected with an impact 
resistant covering, q { should be treated as an opening. For 
positive internal pressure evaluation, q L may conservatively 
be evaluated at height h (qt = #/,). 

C6.5.12.3 Design Wind Load Cases. Recent wind-tunnel 
research [C6-93-C6-96] has shown that torsional load 
requirements of Figure 9 in ASCE 7-98 often grossly 
underestimate the true torsion on a building under wind, 
including those that are symmetric in geometric form and 
stiffness. This torsion is caused by nonuniform pressure on 



Minimum Design Loads for Buildings and Other Structures 



291 



the different faces of the building from wind flow around 
the building, interference effects of nearby buildings and 
terrain and by dynamic effects on more flexible buildings. 
The revision to load cases two and four in Figure 6-9 
increases the torsional loading to 15% eccentricity under 
75% of the maximum wind shear for load case two (from 
ASCE7-98 value of 3.625% eccentricity at 87.5% of 
maximum shear). Although this is more in line with wind- 
tunnel experience on square and rectangular buildings with 
aspect ratios up to about 2.5, it may not cover all. cases, 
even for symmetric and common building shapes where 
larger torsions have been observed. For example, wind- 
tunnel studies often show an eccentricity of 5% or more 
under full (not reduced) base shear. The designer may wish 
to apply this level of eccentricity at full wind loading for 
certain more critical buildings even though it is not required 
by the Standard. The present more moderate torsional load 
requirements can in part be justified by the fact that the 
design wind forces tend to be an upperbound for most 
common building shapes. 

In buildings with some structural systems, more severe 
loading can occur when the resultant wind load acts 
diagonally to the building. To account for this effect and 
the fact that many buildings exhibit maximum response in 
the across-wind direction (the Standard currently has no 
analytical procedure for this case), a structure should be 
capable of resisting 75% of the design wind load applied 
simultaneously along each principal axis as required by case 
three in Figure 6-9. 

For flexible buildings, dynamic effects can increase 
torsional loading. Additional torsional loading can occur 
because of eccentricity between the elastic shear center and 
the center of mass at each level of the structure. The new 
Eq. 6-21 accounts for this effect. 

It is important to note that significant torsion can 
occur on low-rise buildings also [C6-94] and therefore 
the wind loading requirements of Section 6.5.12.3 are now 
applicable to buildings of all heights. 

As discussed in Section 6.6, the Wind-Tunnel Method 3 
should always be considered for buildings with unusual 
shapes, rectangular buildings with larger aspect ratios, and 
dynamically sensitive buildings. The effects of torsion 
can more accurately be determined for these cases and 
for the more normal building shapes using the wind 
tunnel procedure. 



SECTION C6.6 
METHOD 3 - WIND-TUNNEL PROCEDURE 

Wind-tunnel testing is specified when a structure contains 
any of the characteristics defined in Section 6.5.2 or when 
the designer wishes to more accurately determine the 
wind loads. For some building shapes, wind-tunnel testing 
can reduce the conservatism due to enveloping of wind 
loads inherent in Methods 1 and 2. Also, wind-tunnel 



testing accounts for shielding or channeling and can more 
accurately determine wind loads for a complex building 
shape than Methods 1 and 2. It is the intent of the Standard 
that any building or other structure be allowed to use 
the wind-tunnel testing method to determine wind loads. 
Requirements for proper testing are given in Section 6.6.2. 
Wind-tunnel tests are recommended when the building 
or other structure under consideration satisfies one or more 
of the following conditions: 

1. has a shape which differs significantly from a uniform 
rectangular prism or "box-like" shape, 

2. is flexible with natural frequencies normally below 
1 Hz, 

3. is subject to buffeting by the wake of upwind 
buildings or other structures, or 

4. is subject to accelerated flow caused by channeling 
or local topographic features. 

It is common practice to resort to wind-tunnel tests 
when design data are required for the following wind- 
induced loads: 

1 . curtain wall pressures resulting from irregular geom- 
etry, 

2. across-wind and/or torsional loads, 

3. periodic loads caused by vortex shedding, and 

4. loads resulting from instabilities such as flutter 
or galloping. 

Boundary-layer wind tunnels capable of developing 
flows that meet the conditions stipulated in Section 6.4.3.1 
typically have test-section dimensions in the following 
ranges: width of 6 to 12 ft (2-4 m), height of 6 to 10 ft 
(2-3 m), and length of 50 to 100 ft (15-30 m). Maximum 
wind speeds are ordinarily in the range of 25 to 100 mph 
(10-45 m/s). The wind tunnel may be either an open-circuit 
or closed-circuit type. 

Three basic types of wind-tunnel test models are com- 
monly used. These are designated as follows: (1) rigid 
pressure model (PM); (2) rigid high-frequency base bal- 
ance model (H-FBBM); and (3) aeroelastic model (AM). 
One or more of the models may be employed to obtain 
design loads for a particular building or structure. The PM 
provides local peak pressures for design of elements such 
as cladding and mean pressures for the determination of 
overall mean loads. The H-FBBM measures overall fluctu- 
ating loads (aerodynamic admittance) for the determination 
of dynamic responses. When motion of a building or struc- 
ture influences the wind loading, the AM is employed for 
direct measurement of overall loads, deflections, and accel- 
erations. Each of these models, together with a model of the 
surroundings (proximity model), can provide information 
other than wind loads such as snow loads on complex roofs, 



292 



ASCE 7-02 



wind data to evaluate environmental impact on pedestrians, 
and concentrations of air-pollutant emissions for environ- 
mental impact determinations. Several references provide 
detailed information and guidance for the determination of 
wind loads and other types of design data by wind-tunnel 
tests [C6-4, C6-7, C6-8, C6-33]. 

Wind-tunnel tests frequently measure wind loads which 
are significantly lower than required by Section 6.5 due to 
the shape of the building, shielding in excess of that implied 
by exposure categories, and necessary conservatism in 
enveloping load coefficients in Section 6.5. In some cases, 
adjacent structures may shield the structure sufficiently that 
removal of one or two structures could significantly increase 
wind loads. Additional wind-tunnel testing without specific 
nearby buildings (or with additional buildings if they might 
cause increased loads through channeling or buffeting) is an 
effective method for determining the influence of adjacent 
buildings. It would be prudent for the designer to test 
any known conditions that change the test results and 
apply good engineering judgment in interpreting the test 
results. Discussion between the owner, designer, and wind- 
tunnel laboratory can be an important part of this decision. 
However, it is impossible to anticipate all possible changes 
to the surrounding environment that could significantly 
impact pressure for the main wind force-resisting system 
and for cladding pressures. Also, additional testing may 
not be cost effective. Suggestions written in mandatory 
language for users (e.g., code writers) desiring to place 
a lower limit on the results of wind tunnel testing are 
shown below: 

Lower limit on pressures for main wind force-resisting 

system. Forces and pressures determined by wind-tunnel 
testing shall be limited to not less than 80% of the 
design forces and pressures which would be obtained 
in Section 6.5 for the structure unless specific testing is 
performed to show that it is the aerodynamic coefficient 
of the building itself, rather than shielding from nearby 
structures, that is responsible for the lower values. The 
80% limit may be adjusted by the ratio of the frame load 
at critical wind directions as determined from wind-tunnel 
testing without specific adjacent buildings (but including 
appropriate upwind roughness), to that determined by 
Section 6.5. 

Lower limit on pressures for components and cladding. 

The design pressures for components and cladding on walls 
or roofs shall be selected as the greater of the wind-tunnel 
test results or 80% of the pressure obtained for Zone 4 for 
walls and Zone 1 for roofs as determined in Section 6.5, 
unless specific testing is performed to show that it is the 
aerodynamic coefficient of the building itself, rather than 
shielding from nearby structures, that is responsible for the 
lower values. Alternatively, limited tests at a few wind 
directions without specific adjacent buildings, but in the 



presence of an appropriate upwind roughness, may be used 
to demonstrate that the lower pressures are due to the shape 
of the building and not to shielding. 

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[C6-2] Akins, R.E. and Cermak, J.E. Wind pressures 
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JEC15, Fluid Dynamics and Diffusion Lab, Col- 
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[C6-3] ASCE "Wind forces on structures." Trans. ASCE, 
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[C6-4] Wind Tunnel Model Studies of Buildings and 
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[C6-5] Batts, M.E., Cordes, M.R., Russell, L.R., Shaver, 
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[C6-6] Best, RJ. and Holmes, J.D. Model study of 
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[C6-7] Boggs, D.W. and Peterka, J.A. "Aerodynamic 
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[C6-8] Cermak, J.E. "Wind-tunnel testing of structures." 
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[C6-9] Cheung, J.C.J, and Melbourne, W.H. "Wind load- 
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[C6-14] Eaton, KJ. and Mayne, J.R. 'The measurement [C6-28] 

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[C6-15] Georgiou, P.N., Davenport, A.G., and Vickery, 
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[C6-16] Haig, J.R. Wind Loads on Tiles for USA, Red- 
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[C6-20] Krayer, W.R. and Marshall, R.D. "Gust factors 
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[C6-22] Marshall, R.D. The measurement of wind loads 
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[C6-23] Macdonald, P.A., Kwok, K.C.S. and Holmes, 
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[C6-24] McDonald, J.R. A methodology for tornado 
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[C6-26] Minor, J.E, "Tornado technology and profes- 
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[C6-27] Minor, J.E. and Behr, R.A. "Improving the per- 
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